Bullet Holes and Chemical Residues in Shooting Cases

Journal of Criminal Law and CriminologyVolume 31Issue 4 November-December Article 13

Winter 1940

Bullet Holes and Chemical Residues in ShootingCasesJoseph T. Walker

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Recommended CitationJoseph T. Walker, Bullet Holes and Chemical Residues in Shooting Cases, 31 Am. Inst. Crim. L. & Criminology 497 (1940-1941)

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BULLET HOLES AND CHEMICAL RESIDUESIN SHOOTING CASES

Joseph T. Walkert

Several new and important objec-tives are introduced when the medico-legal post-mortem examination of thevictim of a gunshot injury is under-taken. In ordinary practice an autopsyis performed to secure information ofmedical or scientific interest. In medico-legal practice it is performed primarilyto determine, for legal purposes, thecause of death. Although both of theseobjectives are important, many medicalexaminers and investigating officers areunfamiliar with certain potentially richsources of information which are ex-tremely useful in the investigation ofthe crime. To determine the cause ofdeath is, of course, fundamental. Butto determine, insofar as possible, thecircumstances surrounding the fatalacts is often more useful in the admin-istration of justice. Among others, an-swers to the following questions shouldbe sought. Was the wound producedby a bullet? Could the injury havebeen self-inflicted? From what direc-tion was the shot fired? How far wasthe gun from the victim when the shotwas fired? What kind of ammunitionwas used? What kind of firearm wasused?

The answer to these and other ques-tions may depend entirely upon the ex-amination of the body and clothing ofthe victim. With the legal status ofevidence of this kind already estab-lished in the higher courts (27), its

t Massachusetts State Police, and Departmentof Legal Medicine, Harvard University.

value in reconstructing the circum-stances surrounding the shooting andin apprehending the responsible per-son can hardly be over-estimated.

Observations bearing on the answersto questions proposed in the precedingparagraph fall in three categories.

In the first category are the physicalcharacteristics of the wounds. Excel-lent descriptions of wounds are to befound in many of the more recent text-books on legal medicine (84) (85).These include descriptions and illustra-tions of the differences between woundsof exit and entrance; the characteris-tics of the shot canal which indicate thedirection of flight of the projectile; theevidences of explosive effects as are tobe seen in contact shots; peculiaritiesof wounds attributable to the form andvelocity of the bullet which producedthem; peculiarities of wounds producedby spent bullets or bullets in ricochet.

In the second category are the iden-tifying features of bullets found in, orshell cases found near, the body. Thematching of bullets or shell cases forthe identification or exclusion of ques-tioned weapons constitutes a highlyspecialized science which has been ade-quately presented by many authors(83).

It is with the third category of ob-servations that this paper is principallyconcerned. This has to do with theidentification and interpretation of resi-dues of powder, lubricants, and metalswhich may be found on the skin or

[ 497 1

JOSEPH T. WALKER

clothing of the victim, or in the wounditself. It is necessary first to considerbriefly the components of the firearm

and the cartridge in order to appreciate

the significance of these residues.

Firearm: For the purposes of this

discussion only hand firearms (revol-

vers and automatic pistols) will be in-

cluded. The barrel is generally made

of iron or steel, rifled with from fourto seven lands and grooves, twisting

to either the right or left. Frequently

it is fouled from previous shots,rusted, or oiled. Examination of the

interior will usually disclose the

presence of metal fragments de-rived from previous shots embedded

in the depressions of the gun bar-

rel. This is particularly true nearthe breech where erosion of the barrelis likely to be greatest (86) and where

the surface of the bullet has been sub-jected to the greatest stress at its cir-

cumference. Here the metal may oftenbe seen to lie in strips at the edges of

the lands which impart the rotational

thrust to the bullet. Moreover, foul-

ing from the powder charge and primer

charge is frequently present and can be

easily proved chemically. It is there-

fore possible that a bullet fired fromsuch a gun may carry with it traces of

any or all of the materials present on

the interior of the gun barrel-iron,

rust, oil and metals, as well as powder

and primer fouling of previous shots.

Cartridge Case: The cartridge case inmost instances is of brass. Within re-

cent years the primer cap at the base

of the cartridge has been nickel-plated.

Occasionally one also finds the brass

case nickel-plated.

Bullet: The bullet from an automa-tic pistol cartridge generally consistsof a lead core covered with a gilding

metal jacket (copper alloyed with 5 to10% of zinc). This jacket may be bare orplated with tin, or, rarely in this coun-

try, nickel. A bullet of this type isdesignated as "full metal-jacket." Incartridges designed for revolvers the

bullet is generally soft. It may be com-

posed of relatively pure lead, leadplated with a thin layer of copper, or

lead alloyed with antimony, tin, or withboth antimony and tin. Spectrographic

analysis of lead bullets shows the pres-ence of other elements in traces: cop-

per, bismuth, silver and, occasionally,thallium (18) (75). Some revolverbullets have a copper or plated jacketextending about halfway back fromthe tip to the base. The soft metal ofthe core is exposed on the circumfer-ence of the bullet near the base. Inothers, such as hollow point and softpoint bullets, the jacket covers the baseand cylindrical portion, leaving softmetal exposed at the tip. In all bullets,including jacketed bullets, the softmetal of the core is exposed at thebase, or at the tip, or both.

Lubrication: In general lead bulletsdesigned for revolvers are lubricatedby means of a semi-solid waxlike lubri-cant. Jacketed bullets designed for au-tomatic pistols are not so lubricated(36). Spectrographic analyses con-ducted in this laboratory have shownthat the lubrication is generally con-taminated with lead, either mechanic-ally or by the formation of lead com-pounds.

BULLET HOLES AND CHEMICAL RESIDUES

Powder: Formerly the propellantcharge in a cartridge was composed ofblack powder. Since the introductionof smokeless powder, black powdercharges have gradually disappeared,until at present it is rare to find blackpowder cartridges. Black powder isa mixture of about 75% potassium ni-trate, 15% sulfur and 10% charcoal.Upon explosion it yields as solid resi-dues mainly potassium sulfate, potas-sium sulfide and potassium carbonate,together with traces of the originalcomponents and nitrites, thiocyanates,and thiosulfates (39) (68).

Smokeless powder is composed es-sentially of cellulose nitrate (singlebase powder) or cellulose nitrate withnitroglycerine (double base powder)(68). The powder grains are generallycoated with graphite and are in theform of disks or squares. Upon explo-sion, smokeless powders leave verylittle solid residue. That which is leftconsists of carbonized matter or graph-ite in the form of a fine dust and un-burned or partially-burned grains ofpowder, ranging in size from largevisible particles to fine dust. Nitritesand cellulose nitrate are the detectablechemical entities in this residue.

Primer: Some years ago a typicalprimer mixture contained mercury ful-minate, stibnite (native antimony sul-fide), potassium chlorate and powderedglass. Subsequently attempts weremade to eliminate mercury and to re-duce the rust-producing properties ofthe residue of potassium chlorate. (26).

This has resulted in the production ofprimers in which the mercury has been

partially or entirely replaced by lead

compounds, including lead azide andlead styphnate; and potassium chloratehas been replaced by barium nitrate.So where the residue of an old typeprimer characteristically contains mer-cury and potassium, the residue of amodern primer characteristically con-tains lead and barium. Antimony inthe form of stibnite is generally foundin both old and new primers. Zirconiummetal is the latest element to be en-countered. Recent analysis of theprimer residues of ninety-six makesand types of cartridges representingboth old and new ammunition withblack and smokeless powder showedthat the following elements were pres-ent in the percentage of residues in-dicated.

Percentage ofElement Primer Residues

Barium ................ 90%Antimony .............. 87%Lead .................. 75%Mercury ............... 67%Potassium .............. 31%Tin .................... 9%Manganese ............. 4%Zirconium .............. 1%

Subsequent information received fromcartridge manufacturers indicates thattin compounds are not incorporated inprimer mixtures, as the spectrographicanalyses of the residues above wouldimply. Primers leaving tin in the resi-due of the explosion were thereforeremoved from the cartridges by themethod of Chamot (82). In each in-stance the primer compound was foundto be sealed into the cup with a smalldisk of soft metal foil. The foil wascomposed of a lead tin alloy, weighingabout 10 mg The disintegration ofthis foil upon firing doubtless gave rise

JOSEPH T. WALKER

to the tin and a considerable portion ofthe lead in the residues from theseprimers.

To summarize, then, it may be ex-

Substance

pected that the following substanceshaving origin in the gun barrel andcartridge may on occasion be expelledwhen the bullet is fired.

Source

Rust, Iron ................... XLead ................................ XXXTin .............................. XAntimony .......................... XXMercury ............................ XNickel .............................. XCopper ......................... XZinc ................................ XBarium ............................. XXPotassium .......................... XXCarbon ............................. XXNitrates ............................ XXNitrites ........................... XSulfides ............................ XSulfates ............................ XCarbonates ......................... XThiocyanates ....................... XThiosulfates ....................... XLubricating grease ................ XXCellulose nitrate ........................

Note: XXX-Characteristically present.XX-Frequently present.

X-Occasionally present.

22,

M oo A4 V di

di ti 0w

U ct P Pi2 M~ W n. U1 a.

XXXXXXX

X

XXXXXX

XXXX

XXX

XXX

XXXX

XX

XXXXXX

XX

XXXXXxxx

XXXX

XXXXX

..... x

XXX

X

XXx

XXXX

XXXXXXX

The cross marks indicate the author'sestimate of the frequency with whichthe particular substance occurs in thesource mentioned. They have no exactquantitative significance.

In practice it is not to be expectedthat these substances will be intimatelymixed and form a homogeneous pat-tern when fired from a weapon. Ratherit is to be expected that due to their

original differentiation, their variousstates of division and various densities,they will tend to form separate and dis-tinct patterns. This has indeed beenshown to be the case by numerous ob-

servers. It is largely upon the basisof the separate characterization of thesepatterns that valuable information canbe obtained.

Is the Hole a Bullet Hole?

This question is apt to arise in everyshooting case. It is a particularly im-portant one when there are more holes

in the clothing than can be accountedfor by the number of shots believed tohave been fired, or when the numberof wounds in the victim is not in agree-ment with the number of holes in the

clothing.


The question is to be answered uponevidence of two general types: (a) thenature of the damage produced in thematerial under examination; and (b)the presence or absence in it of tracescharacteristic of a bullet. Evidence ofthe first type is of a physical nature;that of the second type, chemical.

The initial entrance of a bullet intofabric is generally circular or elliptical,depending upon the angle of fire. Ifthe bullet has been unbalanced in flight,it may strike with a wobble or endover end; in either case, the hole islikely to be irregular in form. Thesize of the bullet hole is only roughlycharacteristic of the caliber of thebullet. If the bullet has met the fabricobliquely, the latter may be abradedon the near edge to present an appear-ance similar to that of moth-eaten area.This appearance is frequently encount-ered in loosely-woven woolen garmentsor garments bearing a definite nap.

The exit of a bullet through clothingis characteristically irregular in shape.The bullet is generally traveling withmuch less velocity and frequently tip-ping end over end. Such an exit holeis not generally characterized by anabraded area.

The most outstanding characteristicof initial bullet entrances is the pres-ence of chemical substances wiped offthe bullet during its passage throughthe fabric or tissue in question. Thesesubstances compose a dark depositknown as the contact ring around therim of the hole. On dark or blood-stained garments it is not often visibleto the naked eye. The contact ring ismore intense with shots fired from a

dirty or oily barrel than from a cleanbarrel (5) (71). If the shot is a closeone, powder grains and particles ofwax lubrication may be seen adheringto the fabric or skin. With very closeshots a dark smoke halo is presentaround the hole. However, it is onlyunder the most favorable circumstancesthat these deposits are readily detectedwith the naked eye. Dark fabrics,bloodstained and dirty, tend to obscurethis type of evidence. To obtain thefullest information it is generally neces-sary to resort to one or more of thefollowing useful methods: infraredphotography, radiography, spectrogra-phy, or microchemistry.

Infrared Photography: It has beenpointed out by Schwarz and Boler (63),Manczarski (40) (41), Elbel (11) andBeil (2) that many of the products ofcombustion of both black and smokelesspowders are opaque to infrared light,and that by the use of infraredsensitive photographic plates and infra-red filters the dark contact ring andsmoke halo may be readily photo-graphed, even on dark or bloodstainedfabrics. The method is also applicableto skin. The advantages of the use ofthis procedure are more apparent inactual cases than experimentally, forits reliability is manifested under agreat variety of disturbing conditions,among the most frequently occurringof which is the presence of blood anddirt around the hole. Moreover, it isno more difficult and scarcely moretime-consuming than ordinary photog-raphy. The garment is in no way al-

tered and a permanent visual record isobtained.

-JOSEPH T. WALKER

Radiography: As early as 1915,Demeter (8) employed X rays for thedetection of lead in the path of a bulletthrough tissue. Eidlin (10) and Man-czarski (40) have shown recently thatby the use of soft X rays it is possibleto radiograph the metallic deposits infabric or tissue surrounding bulletholes. Since these deposits are verythin, it is necessary to resort to raysof very low penetrating power. Thisrequires the effective use of potentialsof 20,000 volts or less. The ordinaryX-ray tube, immersed in oil and witha heavy window, will not emit rays atthese low voltages. Consequently itis necessary to use a specially designedtube, such as the Grenz-ray tube of theWestinghouse Company. At our sug-gestion, Mr. H. F. Sherwood of theEastman Kodak Company applied thestereo-Grenz ray technique, which hehad previously successfully employedin the examination of fabrics and otherthin objects (65) to this problem. Hisresults have amply confirmed the workof the earlier authors and have indi-cated that the stereo-technique will aidin characterizing the metal deposits. Ithas been shown that the contact ringis rich in metal if the bullet is a softone. This method, like the method ofinfrared photography, is simple anddoes not destroy or alter the materialin evidence. It likewise produces apermanent pictorial record represent-ing the spatial distribution of one classof elements contributed by the bulletto the object struck. Unfortunately,the equipment is not generally avail-

able.Spectrography: Gerlach and Gerlach

(18) (19), Bayle and Amy (1), Buhtz(7), Schwartzacher (64), Walker (75)and Sanni6 (59) have used spectro-graphic methods in detecting metals inthe contact ring and smoke halo aroundbullet holes. It has been shown that bythis means it is possible to detect leadand frequently other metals around theentrance of a bullet into fabric. Thespectrographic methods have the ad-vantage that they are sensitive andrapid. However, a portion of the fabricmust be destroyed.

Microchemical methods: Lochte (35)(36) (37) (38), Jansch and Meixner(28), Briining and Schnetka (5), Hol-sten (24) (25), Schmidt (60) andErhardt (12), and others also, haveemployed microchemical methods todetect various metals around the bullethole. By these means lead, copper,antimony, tin, mercury, nickel and zinchave been demonstrated. These meth-ods, sensitive as they are, require con-siderable technical skill, are frequentlylaborious, and suffer from the disad-vantage that they are not graphic. Aswith the spectrographic method, a por-tion of the fabric must be destroyed.

Has the Hole Been Caused by theEntrance Or Exit of a Bullet?

Clearly, the presence of a detectablepowder residue pattern or a definitesmoke halo or particles of bullet metalor bullet lubricating waxes in a widearea surrounding the bullet hole is eachan indication that the hole in questionis an entrance. However, when theshot has been fired at a distance thistype of evidence is not present. Theonly indications are to be found on the


rim of the hole, where either the effectsof the mechanical action of the bulletor the chemical traces left by the bulletare evidence.

As might be expected, the fibers atthe edge of the bullet hole are fre-quently pressed through the hole in thedirection of passage. This finding isnot sufficiently constant, however, tobe considered with any degree of assur-ance. The explosive action of thebullet and gases in some instancescauses a reversed appearance (73).Generally the clothing has beenhandled before the expert has accessto it, in which case any conclusions asto direction based on the direction ofthe fibers must be regarded with greatskepticism. More significant, however,is the occasional abrasion or moth-eatenappearance of the fibers on the nearside. In tracing the path of the bulletthrough the clothing and through thetissues, materials dislodged by thebullet near the entrance are depositedalong the path in the direction of theexit. Thus Strassmann (70) (71) (73)emphasizes the fact that upon micro-scopic examination fibers abraded fromthe garments will generally be foundin the tissue of the entrance wound inthe body. No such fibers are to befound in the exit wound, except wherethe shot canal is very short (43).Fragments of bone and tissue will fre-quently be found around the exit holein clothing. However, this appearancesometimes occurs also in entranceswhen the explosive action of the gasesor projectile causes a back-splashing ofthese substances (73).

The most characteristic feature of the

initial entrance of a bullet into clothingor tissue is a dark contact ring, madeby the physical contact of the bullet(8) (10) (11) (40) (72). This ring

may not easily be observed on a darkor bloody fabric. Meixner (42), amongothers, has emphasized that the con-tact ring at the entrance wound in skinmay be simulated by a ring at the exithaving an entirely different origin. Hebelieves the exit ring to be caused bythe stretching of the skin beyond itselastic limit, coupled with subsequentincreased drying. Strassmann (72)and others (5) (10) (49) have shownthat the darkness of the contact ring islargely due to gun barrel oil and foul-ing carried on the surface of the bullet:a jacketed bullet fired from a cleanbarrel leaves very little residue aroundthe bullet hole. In confirmation of this,it has been shown by Walker (75) thata bullet fired from a black powdercartridge through a clean gun barrelleaves very little potassium around thebullet hole. However, subsequent bul-lets fired from smokeless powder car-tridges through the same gun barrelwithout intermediate cleaning leaveabundant but decreasing amounts ofpotassium. This experiment provesthat gun barrel fouling contributes asignificant portion of the material ofthe contact ring. The residues of prev-ious discharges, lodged as fouling in thegun barrel, are swept out by the bullet,transported on its surface, and de-posited on the first suitable objectstruck by it.

Lochte (36) and Demeter (8) were

the first to show that the contact ring

was in part composed of metals. In

JOSEPH T. WALKER

the case where a lead bullet was in-volved, they proved the existence ofa heavy deposit of lead at the entrance,with scattered fragments throughoutthe entire shot canal and at the exit.Other authors (1) (7) (10) (12) (59)(60) hive confirmed these results. As

Eidlin (10) points out, metals may orig-inally be derived from either (a)the bullet, (b) gun barrel fouling, or(c) the primer. To this may be added(d) powder (15) (75), and (e) car-

tridge case (12) (15).Eidlin (10) finds that the metals of

the contact ring are largely derivedfrom fouling of the barrel. Bulletsfired from new and clean weapons failto give a typical radiographically-de-tectable deposit of metals around thebullet hole. Upon the basis of spectro-graphic analyses of contact rings fromlead shots, Buhtz (7) concludes thatthe lead present in the ring is derivedfrom the particular bullet in only thesmallest degree. From similar evi-dence, Walker (75) believes that thefollowing factors are responsible, in de-creasing importance: (1) the bullet;(2) gun barrel fouling; (3) metalliccontamination of powder; (4) primerresidues. It is very.probable that theextent to which the metals fromthe bullet or fouling are deposited onthe object struck will depend on boththe hardness of the bullet metal and thehardness and abrasive qualities of thetarget. The X-ray method is most suit-able for the graphic demonstration oflead, but it generally fails to show adeposit when jacketed bullets are used

(10).For the chemical demonstration of

metals, two general methods have beenused-microchemical and spectrograph-ic. Earlier atempts to detect hardjacket metals, such as copper, zinc,nickel, by chemical methods in the con-tact ring often failed (8) (37). Eventhe detection of lead was not alwayssuccessful. Briining (5) has reviewedthe more recent methods by which itis generally possible to detect lead andfrequently the metals of jacketed bul-lets. These methods, employing di-phenylthiocarbazone for lead and zincand rubianic acid for copper and nickel,are sensitive to a few micromilligramsof the metal sought. However, asSanni6 (59) points out, cloth frequentlycontains considerable quantities of allof these metals. The mere presence ofany of these metals around a bullethole is without significance; it must bethere in appreciably greater quantitiesthan elsewhere to indicate a bullet en-trance. Even in the case of lead bul-lets, where the deposit of lead aroundthe entrance is often very great, caremust be exercised. Lead is oftenscattered throughout the shot canal, asBuhtz (7), Demeter (8) and Schmidt(60) have shown. Eidlin (10) feelsthat the distribution of lead about thehole, not its quantity, is the most sig-nificant criterion for the differentiationof entrances from exits. Occasionallya single flake at the exit may containmore lead than the entire deposit atthe entrance. Furthermore, as Schmidt(60) indicates, it is possible that ajacketed bullet might deposit very little

lead at the entrance, split while within,

and leave a heavy deposit at the exit.

The chemical methods for detection


of metals at the orifice, sensitive as theyare, appear to lose much of their use-fulness if not supplemented by a graph-ic method, such as radiography; and,besides, as Sanni6 (59) states, themethods require considerable skill, arenot quantitative, and do not leave apermanent visible result.

Although the spectrographic methodfirst used by Bayle and Amy (1), andsubsequently employed by others, issuperior to the microchemical methodsin several respects, it should be usedpreferably in conjunction with radiog-raphy as a topical (surface) control.Areas may be chosen that are repre-sentative; areas contaminated withforeign matter may be discarded.Where a choice must be made, pictorialmethods are preferable to purelyqualitative or quantitative methods.Any quantitative method, other thanone employing the entire area sur-rounding the bullet hole, is unjustifiedunless one is able to show, by somemeans, that the sample chosen is rep-resentative of the entire area. The dis-tribution of metals around a bullet holeis certainly not uniform. Milovanovie(46) points out that atypical bulletentrances are not uncommon. It there-fore seems advisable that, before anychemical or spectrographic method isundertaken, the bullet hole be radio-graphed to show the distribution ofthe metals being sought.

To summarize the methods of dis-tinguishing entrance from exit holes bythe presence or absence of traces, it

appears that the infrared and soft Xray techniques are the most simple

and the results the most graphic. They

have the advantage that the exhibit isin no way altered. In critical cases thespectrographic method is satisfactory.Where it is necessary to search for onlyone of a few elements, microchemicalmethods are suitable.

From What Distmce Was the WeaponFired?

All methods for the deternination ofdistance are applicable to compara-tively short distances only. Under or-dinary circumstances a bullet woundmay be self-inflicted only when theweapon is held with the muzzle withina few inches of the body. The deter-mination of distance is therefore par-ticularly valuable in this region. For-tunately, fairly accurate determinationsare possible. All available methods de-pend upon the presence and distribu-tion of various ingredients of themuzzle blast. It is therefore necessaryto distinguish carefully between thecontact ring produced in fabric ortissue by the impact of the bullet andthe powder residue tattooing andsmoke halo produced by the muzzleblast. The halo and tattooing are pres-ent only at short distances; the contactring is independent of distance.

There are five major types of mate-rial emitted from the muzzle duringdischarge of the bullet. These con-sist of (1) gases, (2) smoke (finedust, carbonaceous and metallic), (3)residues of partially-burned and un-burned powder, (4) metal fragments ordroplets, and (5) wax or grease lubri-cation.

In order to visualize the processmore readily and to evaluate the sig-

JOSEPH T. WALKER

nificance of each of the above factors,it is desirable to examine the course ofevents within a revolver subsequent tothe moment the firing pin strikes theprimer cap. The primer mixture ig-nites the powder, which underpressure, progressively explodes. Thebullet of lead alloy is forced out of thecartridge case into the barrel. In thecase of a revolver it must pass througha space between the cylinder and thebreech of the barrel. If the chamber isimperfectly aligned with the barrel aportion of the lead of the bullet maybe shaved off. In automatic pistols nosuch action can occur, for the barrelis a prolongation of the chamber. Thebarrel is provided with lands andgrooves which twist either to the rightor left. The bullet, being of a some-what greater diameter than that of thebarrel, is compressed and elongated.At the same time it receives an enor-mous rotational thrust. If the fit of thebullet is not perfect, gases may escapepast it and cause a preliminary dis-charge before it emerges from the bar-rel (68). Subsequent to the emer-gence of a bullet further gases willbe discharged. While this is in prog-ress, the muzzle is describing an up-ward arc around the center of mass ofthe firearm. Thus, in general, matterdischarged before the bullet emergeswould be expected to reach the targetat a point below the bullet hole, andanything discharged afterward, toreach it above (24). Heavy particlesand dense particles might be expectedto carry a greater distance from the

muzzle than light particles and gases.Gases: The gases of combustion, of

both black powder and smokeless pow-der, contain carbon monoxide; the for-mer to the extent of about 10% (68),the latter, 38% (44). Palteuf (51) andMeyer (44), as well as others (23)(57) (69), have shown that with con-tact or near-contact shots, where thesegases enter the body, carbon monoxidehemoglobin is formed from the blood.The shot canal becomes bright red.Spectroscopic proof of carbon monox-ide hemoglobin in the shot canalwould thus serve as a proof of a con-tact or near-contact shot.

Strassmann (70) reported a remark-able case involving a putrified body,which had remained immersed inwater for several weeks. A bullethole at one opening presented abright red appearance, in contrast withthe corresponding orifice and the restof the body, which were greenish. Ina water extract of the tissue of the redregion, "carbon monoxide hemoglobinwas clearly shown spectroscopically".In view of the recent work of Schmidt(61) and others on the stability of car-bon monoxide in putrified blood, itseems more likely that the carbonmonoxide, if present, would be in theform of carbon monoxide hemochromo-gen, or a similar degradation product.Strassmann concluded that the hole wascaused by a bullet fired from shortrange. No powder smoke or powdergrains could be detected.

Smoke: Both black and smokelesspowders give rise to a discharge inwhich carbon and metals are present

as a fine dust or soot. The smoke of ablack powder discharge is much more

dense than that of a smokeless powder


discharge. In either case, if the shot isfired from a comparatively short dis-tance, the fine smoke will be depositedon the target around the bullet hole ina roughly concentric manner. This de-posit may take the form of a halo,showing a greater density near its per-iphery. The diameter and density ofthe smoke halo serve as an indicationof the distance from which the weaponwas fired. In general, a definite smokehalo may be detected under most fav-orable conditions with smokeless pow-der at muzzle distances as great astwelve to eighteen inches, dependingon the type of weapon, the type of cart-ridge, and other factors. B. Miiller (48)believes that an estimate of distancebased on the intensity of blackeningof the smoke halo is preferable to onebased on its diameter. In actual prac-tice it is difficult to measure this in-tensity. With dark and bloodstainedgarments infrared photography hasproved useful (40) (63). Simonin (67)and Brusatto (6) have pointed out thatwith contact shots on skin coveredwith several layers of fabric a modifiedseries of smoke halos or "cocarde" isoccasionally formed within the layersof cloth. In this case the examinationof the outer garment may reveal verylittle in the way of a halo, whereas theinner garments may show several con-centric rings.

It should be noted here that when anautomatic pistol is forcibly pressedagainst the skin at the moment of fir-ing, a dark stamp mark of the outlineof the forward end of the slide may beimpressed around the bullet hole (16)(78). The effect is caused by the re-

turn of the slide to its forward position.This appearance, when present, notonly serves to characterize a contactshot, but in favorable cases may help toidentify the make of pistol. In somecases similar appearances caused byforeign particles in the powder or theejector rod of the cylinder of a re-volver may be encountered (57) (78).

The chemical nature of the smokehalo has been only partially investi-gated. In the case of black powder, itmay be assumed to consist principallyof potassium salts and carbon, althoughit is well known that it is generallycontaminated with lead from the ac-companying lead bullets. Briining (4)has shown that in fresh residues muchof this lead is in the form of sulfide;in older residues, sulfate.

In the case of halos from smokelesspowder cartridges, more work hasbeen done. The halo proper does notnecessarily contain nitrites or oxidizingagents characteristic of unburned orpartially-burned grains of powder (35).A great portion of the dark materialconsists of metals (5), the source ofwhich depends upon a great number offactors.

Many authors have pointed to thestrongly metallic nature of the smokehalo. The earliest metal to be detectedwas quite naturally lead. Lochte (36)was able to dislodge lead particles fromthe area surrounding the bullet holeup to a muzzle distance of Y to 1 m.in all cases where lead bullets wereemployed. By polishing the dislodgedresidues between glass slides or by theuse of X rays, Demeter (8) confirmedthe presence of particles of lead and

JOSEPH T. WALKER

found them to distances as great as12 m. Lochte felt that the lead waslargely derived by the dislodging ofthe bullet from the cartridge case;Demeter, that it came from abrasion inthe revolver barrel. Neither detected

any lead in the bullet hole of shots firedfrom automatic pistols. Demeter notedthat the lead was frequently in theform of gray fluid droplets. Janschand Meixner (28) found lead to a dis-tance of 2 m. by methods similar tothose of Lochte.

Eidlin (10) pointed to the fact thaton the basis of X-ray evidence the leadaround the bullet hole caused by leadbullets fired at short range was in theform of a ring, the diameter of whichincreased with distance. With increasein distance, the ring changed to aninner and outer ring and, in general,became more punctate.

Buhtz (7), employing a spectro-graphic method, found that the quan-tity of lead immediately surrounding abullet hole from a lead bullet de-creased with the shot distance up to200 cm. By the analysis of the fabricaround the hole of near shots, hefound the lead content more dense atthe center, less dense at the periphery.In one experiment, Rankin (58) foundthat the lead content of the cloth of the

bullet hole decreased regularly up to100 feet.

Recently the holes produced in lino-leum by lead bullets fired at closerange from a variety of revolvers wereexamined microscopically in this lab-

oratory. A large number of splashes

of molten lead was found immediatelysurrounding the hole and extending up-

ward above it. The droplets could beseen clearly, even, in some cases, withthe naked eye. Similar shots fired intowoolen cloth left the wool fibers stip-pled with splashes of lead. The dis-position of this lead was certainly notconcentric with the hole. As the dis-tance of the weapon from the targetwas increased to six inches, moltensplashes of lead were still detected,although less were to be observed.This lead appears to originate in theparticular bullet causing the hole. Mi-croscopic examination of the cylin-drical surface of the fired bullet nearthe base at the following edge of eachland impression showed a molten ap-pearance and an apparent loss of mate-rial. That lead bullets tend to meltfrom the action of hot powder gases orfriction within the barrel has long beenknown to those concerned with theirdesign. The presence of splashes ofmolten lead around a bullet hole is,among other things, an indication of anear shot. These droplets, in solid state,probably travel to considerable dis-tances.

The presence of lead in the haloaround a bullet hole is not confined. toshots from lead bullets (5) (18) (24)(25) (59) (60) (75). At the base ofjacketed bullets the lead core is ex-

posed to the action of hot gases. Manymodern primers contain lead in the

form of the azide, dinitrophenylazide,styphnate, thiocyanate, chromate, ni-trate or dinitrobenzoate. The sealingdisk in the primer cup may be com-

posed of a lead-tin foil. It may be

stated that in actual practice lead from

one source or another is present in


the muzzle blast of every type of car-tridge fired in a used gun. Holsten(24) (25) has made use of the general

presence of lead in modern primers toform the basis for the estimation ofdistance based on the quantitative de-termination of this metal in concentricrings around the bullet hole. He em-ployed the sensitive diphenylthiocar-bazone method. Wickenhauser (80)criticized Hoisten's method as inappli-cable to oblique shots. B. Mfiller (48)states that the quantitative determina-tion of lead for the estimation of dis-tance can be expected to be limited toexceptional cases.

Mercury in the form of the fulminateis present in many primer caps, bothold and new. Upon detonation it re-verts to metallic mercury. As early as1907 Georgii (20) observed droplets ofmetallic mercury in the residues ofshots from Flobert revolvers up to amuzzle distance of 20 cm. The pro-pellent powder in cartridges designedfor this firearm was composed largelyof mercury fulminate at that time.Lochte, with Fiedler (37) and withDanziger (38), was able to demon-strate mercury in the halo by chemicalmeans when Flobert cartridges werefired, but detected no mercury withordinary mercury fulminate primedcartridges. Schmidt (60), by a moresensitive chemical procedure, detectedmercury in the later cases to a dis-tance as great as 25 cm. Piedelievre andSimonin (53) and Journi4, Piedelievre

and Sanni4 (29) have been able to

show mercury droplets microscopicallyup to a distance of 20 cm. with

mercury - primed cartridges. Gau-

reschi (17) was unable to dem-onstrate mercury histologically beyond

3 to 4 cm. under similar conditions.Buhtz (7) and Journi6, Piedelievreand Sanni6 (29) have tried the spec-trographic method without satisfactoryresults, although Gerlach (18) claimedthat by employing the method of thehigh frequency spark no difficulty wasencountered.

By a spectroscopic method Gerlach(18) noted in several cases a prepon-derence of iron in the entrance wound.He was unable to establish definitelyits origin and differentiate it fromphysiological iron. Fritz (15) showedthat this iron was in fact due to mate-rial carried on the surface of the bulletor expelled with the powder. In thesmoke halo on the skin it was an indi-cation of a close shot. Fritz used a his-tological method employing potassiumferricyanide in 10% hydrochloric acidas a reagent.

Buhtz (7) was the first to point outthat copper is to be found in the smokehalo of shots fired at short distances.By firing shots from cartridges pro-vided with nickel-jacketed bullets, hefound copper in the smoke halo, butnot in the contact ring. He reasonedfrom this that the copper was derivedfrom the cartridge case. Copper wasfound at distances up to 40 cm. byspectrographic methods. Fritz (15) like-wise detected copper histologically inthe same manner as with iron. Mem-branes of brown copper ferrocyanidewere formed around each particle by

the potassium ferrocyanide reagent.

He found copper up to distances of 20

cm. and concluded from an examina-

JOSEPH T. WALKER

tion of the powder that the copper wasderived from the case. Erhardt (12)determined the copper quantitativelyin the smoke halo in clothing of shotsfired from automatic pistols. The cop-per content decreased with distance upto 20 cm., where it reached the blankvalue for the cloth.

The determination of distance by thequantitation of metals around a bullethole is a process beset with many dif-ficulties. As early as 1915 Demeter(8) observed that the quantity of lead

around the bullet entrance dependsupon the material of the bullet, thelength of barrel, type of target, qualityof barrel wall, construction of weapon,ratio of the caliber to the bullet diam-eter, and form of the bullet, as well asthe distance. And one may add manyother less controllable factors, such asthe cleanness of the gun barrel, themanner of firing the weapon (singleaction or double action with re-volvers), and the angle of fire. In addi-tion there is the almost unsur-mountable difficulty of accurate andrepresentative quantitation withoutdestruction of the entire bullet holeand its surrounding area. The halo israrely, if ever, disposed symmetricallyaround the hole in either form or quan-tity. A preliminary discharge maycause a heavy deposit below the bullethole. An after-discharge creates a de-posit above. The rifling grooves maycause the formation of radiating areasof greater density in the pattern (55).Flakes or chips of the metal in ques-tion, either from the bullet, cartridge

case or fouling in the gun barrel, maycause local accumulations that lead to

an entirely erroneous result. Demeter(8) has shown that individual particlesof bullet metal travel to considerabledistances; in some instances, as greatas 10 m. Obviously, then, one runs therisk of an erroneous conclusion if he at-tempts to determine distance by quan-titation in the smoke halo of a metalwhich is also a constituent of the bul-let. Thus the method of Holsten (24)(25) is applicable only to lead-primed

jacketed bullets.Clothing frequently contains lead,

copper, zinc, tin and nickel (12) (19)(25) (59) (80), in addition to other

metals. If any of these metals is to beused for the purposes of quantitation,the tests must be suitably controlled, ora metal which is not commonly presentin fabric or skin should be chosen. Apossible approach lies in the employ-ment of a metal commonly present inthe primer which is not present in thebullet or cartridge. Barium is such ametal. It has the advantage of notbeing frequently encountered in cloth-ing. In an experiment in this labora-tory conducted to determine the dis-persion of the metallic constituents ofbullet and primer around a bullet holein cloth, a shot was fired at close range,using a cartridge with a lead-antimony-barium primer and a lead bullet. Astrip of cloth 3" wide and extendingfour inches on either side was cutthrough the bullet hole. This strip wasplaced on the flat surface of a 1,S" cop-per bar one-half inch by twelve inches.The bar with adhering cloth was used

as a moveable lower electrode againsta stationary upper copper electrode inthe spectrograph. The copper bar was


moved slowly through the spark whilethe plate-holder of the spectrograph wassynchronously lowered. The resultingspectrogram was a series of overlappingindividual spectra, in effect a progres-sive analysis of a diameter of the smokehalo. It was noted that barium, as wellas lead and antimony, each increased inquantity toward the hole. This methodpromises to be useful for experimentalpurposes. It necessitates destruction ofa portion of the bullet hole.

Lubrication: Particles of bullet lu-brication, present on the surface or inthe cannelure of a bullet designed for arevolver cartridge, may generally befound around the entrance hole inshots at close range from revolvers.These particles are somewhat largerthan powder particles and tend to ad-here tenaciously to rough fabric. Theymay therefore occasionally be found oncloth at a muzzle distance as great asnine feet. By means of a warm iron,Lochte (35) pressed tissue paper covered with blotting paper against thegarment. Lubrication stains producedon the tissue paper were developedwith Sudan III or with iodine or osmicacid vapors.

Powder Residues: Whereas gasesand smoke have comparatively limitedrange, it has long been observed thatindividual grains of powder, unburnedor partially-burned, may travel tosomewhat greater distances. Thus, ifa smokeless powder cartridge is firedinto white cloth, a smoke halo maygenerally be observed up to a distanceof twelve to eighteen inches, whereas

powder grains are likely to be found

as far as twenty-four to thirty-six

inches. The detection of these particlestherefore becomes highly important,for their complete absence tends toplace the weapon outside of the suiciderange. There is one outstanding ex-ception to this generalization, and thatoccurs in the case of the absolute con-tact shbt (66). Here one may find notraces of powder residue on the cloth-ing (54), a fact which might carelesslybe assumed to necessitate a more dis-tant shot. Due consideration to the na-ture of the wound, the appearance offabric at the bullet hole, and in partic-ular the infrared photographs of thesmoke halo or stamp mark of themuzzle will readily enable one to dis-tinguish a contact from a distant shot.Highly characteristic of the contactshot is the cross-shaped tear of thefabric. A like appearance is found onskin (68).

In 1911 Wellenstein and Kober (77),advocated the use of a solution ofdiphenylamine in strong sulfuric acidas a reagent for the characterization ofpowder residue particles. As is now wellknown the reagent is a general one,responding to many oxidizing agents.Its response to powder residues, bothblack and smokeless, is due to thepresence of nitrates and nitrites. Theproduction of the characteristic bluecolor is due to a two-stage oxidation ofthe diphenylamine; the first stage re-sulting in colorless diphenylbenzidine,the second in its blue quinoid deriva-tive (60).

Because of the corrosive nature ofthe sulfuric acid in the diphenyla-mine reagent, the latter cannot be ap-plied directly to the skin or clothing.

JOSEPH T. WALKER

Wellenstein and Kober (77) removedthe powder grains with a needle andtested them on a porcelain plate. Va-rious methods of brushing (22), beat-ing (50) (72), scraping (66) orswabbing (66) the subject to removethe powder grains have been proposed.With but few exceptions, none of themethods is sufficiently graphic to per-mit a reasonable estimate of distance.Strassmann (72) spread that portion ofthe garment containing the bullet holeface down over a tin or wooden vesselwithin which rested a shallow glassdish lined with paraffin. The garment,held in place by means of an outer tinhoop, was scraped or scratched. If thedistance between the garment and theparaffin surface is slight, the dislodgedpowder grains will be found in an im-age of their original location on thegarment. They might then either beexamined microscopically, tested withdiphenylamine reagent, or both. Hil-schenz (22) covered the garment withconcentric rings of cardboard andbrushed out the fabric with a toothbrush, the process being carried outover a dish of diphenylamine reagent.In this way, by successive removal ofcardboard rings and rebrushing, thenumbers of particles at various dis-tances from the bullet hole could beascertained. He found that it was dif-ficult to free the grains from long-fibered fabrics. Dyrenfurth and Wei-mann (9) tried various adhesive baseswith the intent of retaining the re-moved powder particles in their orig-inal relative positions. Cardboard was

spread with (a) glycerine gelatine, (b)

para-rubber solution, or (c) "Mastisol".

The latter was found to be the mostsatisfactory. The cloth was placedagainst this material and beaten; thegrains which adhered were individuallyremoved and tested. Kochel (33)found the above method too laboriousand employed paper spread with waterglass. The diphenylamine reagentcould be aplied directly to this sub-strate with a glass wool brush.

The non-specificity of the diphenyla-mine reagent is a source of great un-certainty (10) (21) (22) (28) (35)(37) (57) (60). Oxidizing agents ca-pable of giving a blue color are com-mon. Clothing very frequently containsthese substances (22) (48) (60).Therefore, with no satisfactory meansof applying the reagent to obtaina true spatial representation ofthe distribution of the grains aroundthe orifice, great caution shouldbe exercised in drawing any con-clusions based upon the finding ofa few scattered particles of a substancewhich responds to the test. On theother hand, the failure to find such par-ticles does not entirely exclude theirpresence. Infrared photographs showthat the brush-out method of removalof powder grains is not complete. Forthis reason Beil (2) believes that theinfrared photography of black powderresidues is superior to the method ofHilschenz (22), particularly when thebullet hole is dirty and when the gar-ment is deep-napped.

Foyatier (13) and others prefer bru-cine in sulfuric acid to diphenylamine.It is more specific for nitrates thandiphenylamine (45). Simonin (66)points out that it has a real advantage


when blue cloth is encountered, be-cause of the fact that the test color isred. Both the brucine and diphenyla-mine reagents suffer from the fact thatthe colors are fugitive; no permanentvisible record of the test can be pre-pared. The choice between the two re-agents appears to be largely a matterof individual preference.

In 1928 Goroncy (21) proposed theuse of alpha naphthylamine and sulfan-ilic acid in acetic acid, for the detectionof nitrites present in the residues ofsmokeless powder. A portion of thecloth is removed and extracted withalcoholic potassium hydroxide. Thesolution is acidified with acetic acid andthe nitrites detected by the productionof a red color on the addition of the re-agent. The depth of color, under con-trolled conditions, may be used as anindication of the approximate distanceof the weapon from the garment. Con-trary to the diphenylamine test, theLunge reagent is specific for nitrites.The test as conducted lacks specificityfor powder residue. The individualgrains are not represented spatially,hence information as to distance is atthe most vague and uncertain. Fur-thermore, a portion of the fabric mustbe destroyed.

Walker (74) has proposed a methodof spatially representing powder resi-

due patterns on fabric by printing thepattern against gelatinized paper treat-ed with "C" acid (2-naphthylamine-4,8-disulfonic acid). Alpha-naphthyla-mine and sulfanilic acid or "H" acid (1-

amino-8-naphthol-3, 6-disulfonic acid)

may be used in the same manner. Fol-lowing is a description of this method:

Ordinary glossy photographic paperis completely desensitized by the usualphotographic hypo bath, washed thor-oughly and dried. It is then immersedin a warm 5% solution of "C" acid forten minutes. The treated paper is al-lowed to dry. A pad of cotton cloth or

a towel is laid upon the table, on top ofwhich a piece of the prepared paper isplaced face up. This must be of suffi-cient size to accommodate all of thepowder residue. On top of this, facedown, is laid the fabric containing thebullet hole. Next are placed a thinlayer of dry toweling, a thin layer oftoweling slightly moistened with 20%acetic acid, and a final thin layer of drytoweling. The whole pack is thenpressed with a warm electric iron forfrom five to ten minutes.

The prepared photographic paperwhen removed is found to have im-pressed upon it a number of dark redspots which correspond to the posi-tion of the partially-burned powdergrains around the bullet hole. This testis sensitive to black and smokelesspowder residue, and is insensitive to allother usual chemicals except nitrites.The test is specific for nitrites andhighly indicative of powder residue ifconsideration is given to the spatial dis-tribution of the particles around thebullet hole. A permanent graphic rep-resentation of the powder residue pat-tern is produced, without in any waydestroying or significantly altering thefabric of the bullet hole. Blood stainsdo not react nor greatly interfere.

There is a general agreement be-

tween authors that in actual cases no

estimate of distance should be made

JOSEPH T. WALKER

without firing a series of test shots fromthe same firearm, with the same type ofammunition and against the same typeof target (32) (33) as were believed tohave been involved in the questionedshot. Great variation exists betweenthe various types and calibers of fire-arms, as well as between the makesand types of cartridges. F. MiUller (49)found that the variations in mechanicaloperation of revolvers greatly affectedthe character of the powder pattern.Employing a revolver of unknownmake, the cylinder of which fitted sopoorly that every time the weapon wasfired part of the bullet was shaved off,Miiller found the powder pattern veryirregular. Scarcely any estimate of dis-tance could be made.

Karhan (30) has investigated the ef-fect of burial and submersion in wateron near-shot characteristics. He findsthat even under the most adverse con-ditions some traces, either chemical ormicroscopic, are likely to be found.

Kraft (34) found that a handker-

chief held over the muzzle did not ap-preciably alter the powder residue pat-tern.

From What Angle Was the Shot Fired?

Any method of graphic representa-tion of the residues surrounding a bul-let hole is capable of being used as ameans for approximating the angle ofincidence of the path of the bullet tothe struck surface. Piedelievre (52)has shown that the more inclined theangle of incidence, the longer the

wound or abrasion. A shot cannot

enter human skin at an incidence angle

of 50 to 100 or less. Moreover, where

a grazing has taken place the greateststrain is produced on the entrance sideof the wound. This last conclusion is inagreement with the X-ray results ofEidlin (10), who found a heavier de-posit of metals in the contusion ring atthe near side of the hole. Furthermore,with near shots an elliptical form to theouter metal ring made visible by X-rayphotography is a means of estimatingthe direction. Elbel (11) points outthat the smoke halo made visible byinfrared photography is also useful forthis purpose. Likewise the C-acidprint test of Walker may be used. Ineach case where the evidence is ob-tained the heaviest deposit is to be ex-pected on the near side of the bullethole. Considerable caution should beexercised, however, for other uncon-trollable factors may give rise to a falseappearance of an angle shot. In esti-mating direction, due considerationshould be given to the fact that theclothing is generally free to swing andassume positions other than that of thesurface of the body.

Wilson (81) has shown in an actualshooting case that a particular revolverregularly left a denser deposit of black

powder residue directly above the bul-let hole. He attributed this phenome-non to a premature escape of the gasesat the top portion of the barrel, due tofaulty manufacture. Although in thisparticular case this explanation mighthold, it is a recognized fact that evenwith well-constructed revolvers the de-posit is more dense above the bullethole. This is attributed to the discharge

of gases subsequent to the emergenceof the bullet. In revolvers the muzzle


describes an upward arc while the bul-let and gases are being discharged; con-sequently the after-discharge is locatedabove the bullet hole (55) (83). Inautomatic pistols the center of masslies near the axis of the barrel. As aresult there is little tendency for themuzzle to rotate upward, and the after-discharge is likely to be found on thetarget concentric with the bullet hole.Whatever the cause, the regular pro-duction of a dense eccentric depositserves as a means of orienting the posi-tion of the weapon with respect to thetarget. In this laboratory it has beenfound that the droplets of molten bul-let-metal likewise are to be found onthe target above the bullet hole. Insome cases they range slightly to theleft; in others, to the right.

Caliber of the Bullet

It is particularly difficult to estimatethe caliber of the bullet from a mereexamination of the hole produced by itin an elastic material, such as fabric orskin tissue. Holsten (24) (25) statesthat the caliber can be estimated innear shots by determining the diameterof the chemically-provable lead-con-taining smoke halo, where lead primercharges have been used. Buhtz (7) be-lieves that the quantity of spectro-graphically-detectable lead in the con-tusion ring is dependent upon distanceand caliber; if one can be determined,the other can be estimated. That thedispersion of the smoke halo elementsand powder residues is dependent uponthe caliber to a certain extent is obvi-

ous, but the other factors involved are

very numerous. It is doubtful if suffi-

cient exact information of these factorswill be available frequently in actualcases.

What Type of Powder Was Used?

In the United States only three typesof powder need to be considered-black, smokeless and semi-smokeless.A black powder discharge is character-ized by a heavy black deposit, inter-spersed with dense black or gray par-ticles, or minute spherical sulfur-col.ored masses. Infrared photographs ofthe pattern will disclQse a typical pic-ture of dense black spots (2). Chem-ical analysis of one of these spots fornitrates, potassium, sulfate and sulfidesdefinitely indicates black powder resi-dues (25) (31) (37) (39) (56) (68).The sulfides which are present in freshblack powder residues are rapidly con-verted into thiosulfates and sulfates.Potassium sulfide is lost after four tosix hours (45). Black lead sulfide (4)from the lead of the bullet and ironsulfide (45) are converted after severaldays into light-colored sulfates. Theseand other changes form a basis for theestimation of time elapsed since a wea-pon was fired (39) (45). A modifica-tion of the C-acid print test can also beemployed if the residue is fresh. In-corporation of lead acetate on the gela-tinized paper will give a pattern ofsemi-metallic spots of lead sulfide.

Smokeless powder residues do notgive a dense black pattern of individualspots when photographed with infra-red light. Neither does the residue con-tain appreciable quantities of potas-sium, sulfates or sulfides. Black pow-

der residues are alkaline to litmus;

JOSEPH T. WALKER

smokeless powder residues are acid (4)(5) (35) (55) or neutral (26) (39).

The acidity of the residue grains isprobably dependent upon the internalpressure during explosion; high bar-rel pressures tend to produce a non-

acid smokeless powder residue. Nippe(50) suggests that the distinction be-

tween black and smokeles powder resi-dues can be confirmed by the fact thatthe nitrates of the former are solublein water. Black powder charges areonly occasionally encountered today.They are never met with in ammuni-tion designed for the automatic pistol.We may expect a lead bullet and a bul-let lubricant where black powder isencountered. As has been shown else-where (75), the presence of black pow-der residue in the contact ring proper,to its exclusion elsewhere, does notnecessitate a black powder charge forthe particular bullet in question. Itimplies a previous black powder chargefired from the same weapon.

Semi-smokeless powder consists ofan intimate mixture of the principalcomponents of both black and smoke-less powders. The proportion is gener-ally 80% black and 20% smokeless. Thegrains of the original powder are dull-black, angular particles resemblingblack powder, except for the lack ofluster and more angular appearance.When fired they leave a residue similarto black powder residue in appearanceand chemical composition. It is doubt-ful if a distinction could be made be-tween the two residues in actual cases,

unless unburned grains happen to bepresent.

One of the most characteristic prop-

erties of the muzzle blast from a blackpowder cartridge is its intense heat.Weimann (76), in a series of experi-ments, showed that singeing generallyoccurred to distances of 20-30 cm. andsometimes to Y m. Tissue and bodyhairs are singed or scorched, and cloth-ing is frequently ignited. In contrastsmokeless powder causes no singeingor burning (10 (14) (22) (35) (44)(57) or at most negligible traces at adistance of a few centimeters (23)(76).

It is possible in some instances todistinguish the various types of smoke-less powder. If the combustion has beenso incomplete as to leave large particles,their form may be recognized (31)(68). In bulk, double base powder maybe distinguished from single base bywarming at 1000 C. in a shallow dishcovered by a watch glass. The nitrogly-cerine vaporizes and condenses as a fogon the watch glass where it may betested with diphenyamine reagent. Amodification of this method has beenfound useful in this laboratory. A frac-tion of a flake of powder or a smallparticle of residue is placed in a capil-lary tube, one end of which is sealed.The tube is evacuated (water pump),sealed, and placed in a copper heatingblock provided with a thermometer. Aportion of the tube is allowed to pro-ject from the block. The block isheated to 1000 C. If the powder isdouble base, nitroglycerine distills intothe cool portion of the tube. It may beobserved under a microscope or testedfor by breaking the capillary underdiphenylamine reagent. It has alsobeen observed that certain smokeless


powders tend to leave very plastic resi-dues. In tests conducted on linoleumwith automatic pistols (no lubrication),splashes of powder residue similar tothe splashes of molten lead were ob-served. When the shots were fired intocloth, the powder residue particles sur-rounded the fibers and assumed thecontour of the surface. So far thisphenomenon has been encounteredonly when double base powders havebeen used.

What Type of Bullet Caused the Hole?

Many attempts have been made todetermine the composition of the bul-let from the metals present in the haloor contact ring. Schwarzacher (64)analysed fragments of metal found inthe vicinity of the bullet hole, whileBayle and Amy (1), Brining (4), Ger-lach (18) (19) and Sanni6 (59) haveanalysed the contact ring with thispurpose in mind. The assumption mustof course be made that the metal de-posits are derived from the surfacemetal of the particular bullet whichmade the hole. That this is not truein the majority of cases has been shownby numerous investigators. Thus. leadaround a bullet hole is often derivedfrom gun barrel fouling or primer resi-dues (7) (24) (25) (60) (75). Cop-per and zinc can as easily be derivedfrom fragments of cartridge case metalas from the bullet jacket (7) (12) (15).Antimony and tin are constituents ofprimers as well as of bullet metal (60)(75). Even nickel around a bullet holedoes not necessarily signify a nickel-jacketed bullet, for the primer caps ofmodern cartridges are nickel-plated.

As has been indicated previously, thesource of the deposit left on the con-tact ring is to a large extent dependentupon thie abrasive qualities of the tar-get. Soft fabric or skin tissue maymerely wipe the loosely-bound foulingfrom the surface of the bullet; bone orabrasive fabrics may remove the bulletmetal. Much will depend upon the cir-cumstances.

It is of course obvious that radiogra-phy of the bullet hole will be helpful.Eidlin found no detectable deposit onthe contact ring in clothing when jack-eted bullets were fired at a distance.If black powder can be proved, a leadbullet is implied. Proof of an auto-matic pistol necessitates a jacketed bul-let.

Was the Wound Self-Inflicted?

Suicide with a firearm held in thehand necessitates a muzzle distance oftwenty-four inches or less. Powderresidues, and frequently metals, lubri-cation and components of a smoke halo,are detectable within this distance. Ab-sence of near-shot traces tends to ex-clude suicide. In shots found to havebeen fired within two feet, due consid-eration must be given to the locationof the entrance and the anatomical pos-sibilities.

It has long been known that powderresidues escape around the breech of apoorly-constructed revolver and are tobe observed occasionally on the handof a person who has recently fired thegun (21) (22) (23) (43) (66). In1922 Benitez (3) recommended theapplication of the diphenylamine re-agent to the interior of a paraffin mold

JOSEPH T. WALKER

of the surface of the right hand as ameans of detecting powder residue par-ticles. B. Mueller (47) recently con-ducted experiments on the presence ofpowder residues on the hand of theperson firing the gun. He came to theconclusion previously reached also byothers (22) (43) that a number of re-volvers give no residue, and that a neg-ative result on the hands of the victimdoes not exclude suicide. The occur-rence of powder residues is largely de-

pendent on the precision with whichthe revolver is constructed. Muellerdid not use the paraffin mold-diphenyla-

mine method of Benitez (3).It should be mentioned at this time

that if it is necessary to exercise cau-tion in drawing conclusions based onthe appearance of a few particles of asubstance which responds to thediphenylamine test on the clothingaround the bullet hole it becomes evenmore important to do so when evalu-ating residues on the hand. Here atmost the number is not great, and thehuman hand is even more liable to becontaminated with foreign substancesthan clothing. Matches and tobacco,among other common things, give apositive diphenylamine test.

Werkgartner (79) mentions the factthat blisters and pinch marks are to befound on the firing hand on occasion,after the use of automatic pistols.Holding the weapon in the right handand supporting it with the left handfrequently leaves blood or powderstains on the left hand. In addition theexplosive action of the gases during acontact shot may blow fragments of

tissue back on the firing hand. Par-ticles of bone may be expelled with

such force as to cause small puncturewounds (78).

Examination of Clothing: ProposedProcedure

In order to employ as many usefulmethods as possible in a single pro-cedure for the examination of a bullethole in clothing, the following sequenceis proposed:

1. Visual Examination. Note sizeand shape of hole, disposition of fibersat entrance, evidence of abrasion, evi-dence of residues.

2. Photography. The use of panchro-matic film is recommended for the rep-resentation of the appearance of thegarment at the hole.

3. Infrared Photography. Use infra-red sensitive plate and Eastman # 88 Afilter to represent smoke halo, blackpowder residue and contact ring.

4. Radiography. Use soft X rays tovisualize deposits of heavy metals insmoke halo and in contact ring.

5. Microscopic Examination. Use bin-ocular dissecting microscope to exam-ine fabric, to locate foreign fibers,tissue or bone fragments in hole, and tofind powder particles. Evidence ofsplashes of molten lead may be seen.

6. Remove questioned traces fortesting. Distinguish black from smoke-less powder. Remove particles of metallocated by radiograph.

7. Press area around hole with tissuepaper under a mildly-warm iron. Lo-cate lubrication traces.

8. Perform C-acid print test for pow-


der residue. Add lead acetate to paperif there is a question of fresh blackpowder.

9. Spectrographic analysis of suitableportion of halo or contact ring as shownby infrared photograph, and radio-graph, or-

10. Microchemical analysis, as an al-ternate or supplement to spectro-graphic analysis, might indicate muzzledistance or type of bullet.

Examination of Wound: ProposedProcedure

1. Visual Examination. Note sizeand shape of bullet hole.

2. Photography. General-view pho-tographs of body as well as individualclose-up views of the wounds. Pan-chromatic film is recommended.

3. Infrared Photography. Use infra-red sensitive plates and an Eastman#88A filter, to represent the smokehalo, stamp mark or contact ring.

4. Removal of Tissue. Remove theskin surrounding the bullet hole.Stretch it on a board with tacks orpins. Remove portions of the bullettract and place them in separate smallbottles or jars, unfixed.

5. Radiography. Trim away subcu-taneous tissue and place on cellophane.Use soft X rays to visualize the metals.

6. Microscopic Examination. Exam-ine the skin and bullet tract under adissecting microscope. Remove ques-tioned metals, fibers or other particlesfor testing.

7. Chemical Analysis. Cut out smallportions of tissue for spectographic ormicrochemical analysis.

8. Cleaning. Wash away the adher-ing blood. Re-examine the skin for evi-dence of tattooing.

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Documents

Bullet Holes and Chemical Residues in Shooting Cases