Henke, Lee K.

Mathews, J. H.

English

Northwestern University Illinois, School of Law: Scholarly Commons

Journal of Criminal Law and CriminologyVolume 35 | Issue 2 Article 111944The Rifling MeterJ. H. MathewsLee K. HenkeFollow this and additional works at: https://scholarlycommons.law.northwestern.edu/jclcPart of the Criminal Law Commons, Criminology Commons, and the Criminology and CriminalJustice CommonsThis Criminology is brought to you for free and open access by Northwestern University School of Law Scholarly Commons. It has been accepted forinclusion in Journal of Criminal Law and Criminology by an authorized editor of Northwestern University School of Law Scholarly Commons.Recommended CitationJ. H. Mathews, Lee K. Henke, The Rifling Meter, 35 J. Crim. L. & Criminology 134 (1944-1945)THE RIFUNG METERJ. H. Mathews and Lee K. Henke(Dr. Mathews is Chairman of the Department of Chemistry at the Universityof Wisconsin. For some years he has been interested in the use of scientificmethods in criminal identification and has developed a number of useful in-struments-particularly in the field of forensic ballistics, of which the riflingmeter described in this article is one. Mr. Henke is Senior Mechanician in theDepartment of Chemistry at the University of Wisconsin and has devoted manyyears to the designing and construction of special apparatus for scientific re-search purposes.-Editor.)Workers in the field of firearms identification often have needof rifling data not presently available in textbooks or referenceworks, or obtainable from gun manufacturers. Not infrequentlya fired bullet is brought in for examination in connection withsome crime. No gun is submitted, nor does a suspect appear athand. In such a situation the first problem, necessarily, is de-termination of the make and type of gun from which the bulletwas or might have been fired. If the law enforcement officer canbe supplied the correct answer as to the identity of the make andcalibre of the gun, the field of search for the wanted gun is nar-rowed and the possibilities of discovery greatly enhanced. Forexample, if it can be shown that the fatal bullet in the case wasfired from a .32 caliber Ortgies automatic pistol and no other,search for all other .32 automatics can be halted at once and thesearch narrowed to the one wanted model.It may appear that the rifling specifications data maintainedby the different gun manufacturers would be of prime assistancein classifying the make and caliber of the wanted gun. In generalit should be said that the various gun manufacturers do havedefinite rifling specifications and the more reliable ones make a realeffort to follow their specifications closely. Now, if each and everymanufacturer had different specifications and continued at alltimes to adhere to them, then by making a few accurate measure-ments on a fired bullet one would know, invariably, from whatmake and type of gun the bullet had been fired.But it is not as simple as that, however. In the first placemany of the cheap foreign made guns are "'assembled" guns, i.e.,the various parts are assembled from parts which have been madein various shops and apparently not from uniform rigid specifica-tions, if indeed from any specifications at all! The identity of themaker of such guns obviously cannot often be determined frommeasurements made on a fired bullet.Another difficulty arises from the fact that from time to timea manufacturer may change his specifications. Hence, the firedbullets will present a different set of data corresponding to thechange. A similar situation confronts the examiner of typewrittenTHE RIFLING METERdocuments. Manufacturers change the font (shape of letters)from time to time. A document dated 1908 allegedly written ona Remington typewriter and having a design of type not manufac-tured until 1916, is clearly fraudulent. Hence these changes inspecifications are very useful. Similarly a change in rifling speci-fications may "date" a gun from which a fatal bullet was fired.Document examiners have accurate records of all changes made intype design by the different manufacturers and the dates ofchange. Unfortunately similar data on changes in rifling speci-fications made by different manufacturers are not available. Oftenthe manufacturers themselves do not have complete data. One ofthe largest of the world's gun manufacturers, for example, hason three occasions had all its records destroyed, twice by fire andonce by flood. American manufacturers have been very coopera-tive in furnishing such information as they have, and there is con-siderable information available on a few of the foreign guns. Someof this latter information is, however, none too reliable, and it isvery unfortunate that following World War I there were heavyimportations of foreign made guns, many of which are found inthe hands of the criminal. If such an accumulation of data as ishere suggested is ever to be made, it will necessitate a great manymeasurements on guns of, all makes, types and vintages. It is ajob which should be done, and it is our intention to make suchmeasurement on all guns which become available to us.The particular information needed to determine the make andtype of gun from an evidence bullet is obtained by noting or meas-uring the following: (1) Width of grooves on bullet (correspond-ing to width of lands in the rifled barrel), (2) Width of lands(corresponding to width of grooves in the rifled barrel), (3)Number of lands and grooves, (4) Degree of slope of the rifling,(5) Direction of this slope (indicating a right or left hand turn),and, in some cases, (6) The depth of the grooves. Of these sixitems the first five are absolutely essential, and the sixth may behelpful. There are available to the identification expert suitablemethods for measuring the angle of rifling on the fired bullet andthe widths of lands and grooves. If a complete file of informationon rifling specifications for all guns were available, the particularmake and type of gun which had fired the evidence bullet couldbe determined, or at least the search could be narrowed down toa very few possibilities. It is true that the specifications for twoguns of different make may quite closely approximate each other,but even narrowing down the search to two, three or even fourpossibilities is very useful.Because of the paucity of information on rifling specificationswe have developed in this laboratory an instrument for meas-uring the pitch of rifling in a gun. This is accomplished byJ. H. MATHEWS AND LEE K. HENKEpushifig a bullet, or preferably a lead disc through the barrel andat the same time measuring the rotation of the bullet for each inch(or half inch) of travel. After the disc is inserted in the end ofthe barrel a "zero" reading is taken. Then the disc is pushed for-ward exactly one inch (for example), and the extent to whichthe bullet has rotated is measured on a graduated circle providedwith a vernier capable of giving readings to 0.050 or 3' of angle.Suppose the rotation is found to be 22.50'. Then at this rate thedistance required for one complete rotation of the bullet will be360-or 16 inches. Naturally several readings are taken and aver-22.50aged. The accuracy of the driving screw calibration and the read-ings of angle are such as to give a reproducibility of results to0.1" on a turn of 16 inches if the rifling in the barrel is in goodcondition. Checks on guns of known rifling specifications havebeen made repeatedly and found to be accurate.After the disc is pushed through the barrel the width of thegrooves and lands on its edge are measured and notations aremade as to the number of lands and grooves and the direction ofrotation. This information, together with the name of manufac-turer, type and model of gun, serial number and name of owner,is recorded on a form card and filed according to the measuredclass characteristics.The instrument consists of three essential parts. The head, thevise, and the bench. For ease of description we shall describeeach part separately.The Head:The head is not unlike the tail stock of a modern lathe. SeeFig. I. It consists of a lead screw threaded left hand and actuatedby a hand wheel. This lead screw is supported by a bronze bear-ing. Bronze was used because of the pressure that is necessaryto start a disc or bullet down the barrel being tested. The leadscrew actuates a steel ram, which has a narrow groove milled itsentire length. A short spline in the front of the ram housingengages with this groove, thus preventing axial rotation of theram when it is moved longitudinally. The threaded bushing inthe ram is also of bronze. The steel ram is graduated in sixteenthswhich are used as a check against the micrometer dial graduationson the sleeve attached to the hand wheel. The lead screw has tenthreads to the inch, and the dial is graduated into 100 divisions.Thus every division on the micrometer dial is equal to one one-thousandth of an inch. At the opposite end of the ram is mounted,by means of a thrust bearing ("Nice" number 1001), a five-inchdial divided into 360 divisions, 180' in each direction from zero.Fig. II. A vernier of twenty divisions is matched to this dial(7~FIGURE IRifling meter with rack at right, contain-ing six of the seven rods used for pushingdiscs through barrel of hand gun beingcatalogued.FIGURE IICloseup of rifling meter showing muzzle of gun without clamp, and thequadrant at the right which permits measurement of angular rotation of leaddisc being pushed through barrel being measured.FIGURE IIIRifling meter head stock with barrel in place and supplementary clampreferred to in text.FIGURE IVPunch and extra dies for cutting 1/16 inch lead discs for rifling meterTHE RIFLING METERgiving readings to .050. Attached to the thrust bearing is a socketinto which the several sizes of push rods fit. This socket has atapered fiat key so that when the push rods are inserted therewill be a positive fit with no danger of axial rotation of the pushrod in its socket. Each push rod is equipped with two diametricallyopposite piano wire pins whose ends are ground wedge-shaped toprevent axial rotation between the base of the bullet or disc andthe push rod face.Above the ram housing are mounted two magnifiers, one overeach micrometer as can be seen from the photograph. Over thevernier is another magnifier on a swivel mounting, so that thevernier can be read in either direction to take care of both rightand left hand riflings. The entire head ensemble is held down bytwo knurled and slotted nuts, so that by loosening them the entirehead can be shifted along the bench to any desired position, andthen firmly clamped to the bed of the bench.The Vise:The vise consists of a pair of parallel jaws faced with Celeron,to prevent damaging the barrels clamped in it. Two guide rodsare used to keep the jaws in alignment. The jaws are given abi-lateral movement through the use of a lead screw threadedboth right and left hand from center. This lead screw terminatesin a steel handle having two holes so that a spanner wrench maybe used to tighten the barrels in place. Down the center of the"Celeron" facings, whose surfaces are cross hatched, is cut a fairlydeep "V" groove to facilitate the centering of the barrel beingmeasured. The vise body is capable of vertical adjustment bymeans of a dovetailed inclined plane and actuated by a fine leadscrew whose shaft terminates in a knurled knob. After an adjust-ment is made the vise can be locked permanently in position bymeans of a "V" shaped wedge which is tightened or loosened bymeans of a thumb screw. The entire vise parts are enclosed ina heavy steel housing which in turn is fastened permanently inposition on the end of the bench.The Bench:In order to eliminate the time necessary for a good casting toage and become usable as a bench, it was fabricated fromtwo pieces of channel iron selected for straightness and mountedthe desired distance apart by means of spacing blocks held in posi-tion by heavy machine screws. The feet were then attached anda light cut was taken across the top from end to end. The benchwas then checked with a dial indicator and the high spots marked.These were removed by hand scraping until a good surface waspresented. Later when the head assembly was placed in positionthis was also filed and hand scraped until by checking with boththe indicator and a good straight edge no tolerance greater thanJ. H. MATHE"WS AND LEE K. HENKEone-half thousandth was observed. Because the channels werefacing each other they left a space between them which was util-ized to help center the head assembly when being moved longi-tudinally. A spanner wrench was made to fit the vise and anotherwrench was made to fit the slotted nuts.The push rods are about five thousandths of an inch less indiameter than the calibre of the gun with which they are to beused. This diameter is maintained for a distance of about threethirty-seconds of an inch back from the tip of the rod that comesin contact with the base of the bullet or disc, the remainder of therod has its diameter reduced by about twenty thousandths so thatat no time can there be contact between the gun barrel and thepush rod.Because the outside of barrels encountered are tapered and oddshaped, an auxiliary split steel clamp was constructed having splitbrass inserts which are interchangeable with each other.- Theseinserts have a hole through them closely approximating the barreldiameter. In practice this clamp is placed over the barrel beingtested just back of the front sight. The back of this clamp thenrests against the front edge of the vise taking most of the pressureexerted. Consequently the vise itself does not have to be clampedwith such heavy pressure as would be the case without the auxiliaryclamp. This accessory is not shown in Fig. No. I but is shown inFig. III. Nine sets of inserts for various sizes and types of barrelshave been found to accommodate all barrel shapes encountered.Punch and Die Set:A very desirable accessory to the rifling meter is a punch anddie set, such as the one illustrated in Fig. IV. This is used forcutting the lead discs which are to be pushed through the barrel.Lead bullets were first used but these became unobtainablebecause of war restrictions. This turned out to be a fortunatecircumstance as the lead discs were found to work much betterthan lead projectiles. Discs cut by steel dies have accurate, repro-ducible diameters whereas the diameters of purchased bullets varyconsiderably. Furthermore, the rifling meter gives the best resultswhen a moderate pressure is required to force the lead objectthrough the barrel. Bullets present a very considerable surfaceof contact with the walls of the barrel and a slightly over sizebullet will require considerable pressure. This is not desirable.Lead discs cut from 1/16" sheet lead present much less, but suffi-cient, surface and require only a moderate pressure. Measure-'We are greatly indebted to Mr. Jacob Menn, a student in chemistry at theuniversity for assistance in the construction of the auxiliary clamping deviceand the press for cutting discs. Mr. Menn has also made a large number ofmeasurements with the rifling meter.THE RIFLING METERments obtained by the use of discs have proven to be much morereproducible and more accurate.Since there are many calibers it is necessary to have a consider-able number of pairs of dies and punches. Indeed a number ofpairs are necessary for the caliber known as .38 since these varyall the way from about .35" to .41". For the other calibers thevariation is small and usually one pair will suffice.The punch and die set illustrated consists of a heavy base plate,semi-circular in shape upon which is mounted a heavy columncarrying the punch holder and the operating lever. The dies areset in a secondary heavy steel platform having a series of holesarranged in an arc described by the rotation of the punch holder.The position of each die is such that the punch comes into perfectalignment over each die.The punches and dies are made in pairs for any given caliberand are readily interchangeable. The dies are locked in place byheadless Allen screws. Both dies and punches are fabricated fromhigh speed drill rod, hardened, tempered and ground. Three de-grees clearance -&." below the cutting edge on the dies and 0.005"relief 1/ " back of the cutting edge is used on the punches. Alloutside diameters of the shanks of the punches are identical andthe same is true for the dies, so that there may be interchange-ability.Some of the sizes of the punches found to be most useful aregiven below:.2277" .3576".2573" .3790".3055" .4043".3095" .4398".3177" .4556"The *9w" sheet lead used for raw stock for the discs is readilyobtainable and causes no appreciable wear on the punches or dies.If wear occurred, the punches and dies could be easily sharpenedin any shop equipped with a small lathe tool post grinder, a fewthousandths face grind being all that would be necessary. Twometal drawers, below the dies, catch the discs. The discs are veryperfectly formed and have clean cut edges. They are easily at-tached to the end of a push rod. After centering the push rod onthe disc a light tap with a fiber faced hammer seats the disc on thepins set into the end of the rod.Such, in brief, is the rifling meter, its structure, use and values.If construction of a rifling meter is contemplated, a set of workingdrawings can be obtained by writing the Authors.

The Rifling Meter

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The Rifling Meter

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