Some general observations regarding bullets

Before the advent of smokeless powder, plain lead or lead hardened by the addition of small amounts of antimony or tin (or both) was used for bullet making. But with the higher velocities attainable with this new powder, „metal fouling" became a serious problem, and this led to the use of surface coating of the lead bullets with some harder metal. Bullets for low powered .22 cal. rifles are still made of plain lead alloy, or they may have an extremely thin protective coating of copper or of some copper alloy which not only hardens but also lubricates the bullet and reduces metal fouling. This thin coating (or gilding) is not to be confused with the „jacketing" of bullets with a metal casing. Many years ago bullets were lubricated by putting grease on their exterior surfaces, but now lubrication, when used, is done by putting the lubricant in a depressed ring (called a cannelure) around that portion of the bullet which is within the case, so that it is held in place and the exterior of the cartridges is free from grease. These cannelures also enable the maker to produce a longer bullet without increasing its weight unduly, and they are frequently used to help hold the bullet in proper position by having the end of the case crimped into one of them. Holding the bullet in proper position is important because if the bullet is set back too far into the case the pressure of firing may be dangerously increased, and if it should move forward and become loosened it would not feed properly into the mechanism of the gun. In some cases, particularly in the older types, there was a shoulder on the lead bullet which prevented the bullet from setting back farther into the case. Jacketed bullets may be held in place in a number of ways. The end of the case may be crimped into a cannelure on the bullet; the case itself may have a cannelure against which the end of the bullet is tightly pressed; the bullet may fit so snugly that it will stay in place; or points (usually three in number) may be „peened" into the case so as to produce increased friction.

Metal-jacketed bullets are now standard for high powered rifles and for use in automatic pistols and machine guns. And they are widely used in revolvers. Many varieties have been developed and a collection of all types is a necessary part of the equipment of a crime laboratory. Unlike the gilded lead bullets, where the coating is not more than 0.0002 inch thick, the jackets are from 0.020 to 0.030 inch in thickness.

For use in automatics the jacketing covers the whole forward end of the bullet and the only exposed lead is in the center of the base end. For hunting purposes the jacket may cover all of the bullet except a portion of the nose end. These „soft nosed" bullets expand on striking flesh and cause more destruction of the tissues, thus increasing their effectiveness (Fig. 18). „Hollow point" bullets are completely jacketed with the exception of a small hole at the point. These open up upon striking flesh and are very destructive to tissues. All bullets for military use are fully covered at the nose end. They may have a rounded nose or they may be very pointed, to produce greater penetration. A steel (or other hard metal) point may be set into the nose end of this type of bullet to further increase penetration.

In the case of both hollow-point and soft-nosed bullets, instances will be met frequently where the only portion of the bullet received by the examiner will be the jacket-the lead core having been completely expelled. Since the rifling marks are on the jacket, this loss of the lead is of no particular importance. For some high powered rifles the velocity of the bullet may be so great that it practically explodes when it strikes an animal (or any other object) and no large fragments of the bullet may be found. Then very small fragments of the jacket should be searched for, because even a tiny piece may carry identifying markings.

Bullets designed for automatic pistols (of caliber higher than .22) are fully metal-jacketed at the nose end, because exposed lead would likely lead to malfunctions. The finding of such bullets (i.e., bullets designed for use in automatic pistols) does not necessarily mean that they were actually fired from an automatic pistol, however. Cartridges designed for automatics can be fired from some revolvers and vice versa, although the practice is not a common one. The only exception to the last statement is the case where „half moon" clips are used to hold .45 cal. A.C.P. cartridges so that they may be used in a revolver in spite of the absence of a projecting rim. All .22 cal. automatic pistols are designed to function with the same ammunition as is commonly used in revolvers, single shot pistols, and rifles.

The jacketing material may be of copper or cupronickel, both of which are much harder than lead. Steel jackets are used to some extent in Europe but are not made in the U.S.-except for experimental purposes. jacketed bullets do not require lubrication and do not (ordinarily) produce metal fouling. Metal fouling does occur to some extent with the „gilded" type of coating, although the protective coating (and lubrication) prevents it considerably. Metal fouling presents a serious problem to the firearms examiner. If a test bullet is fired through a barrel which has become fouled subsequent to the passage of the evidence bullet through it, the markings on the test and evidence bullets may be quite different. Also, if the evidence bullet was fired through a fouled barrel which subsequently had been cleared of all fouling (previous to the firing of a test bullet), the evidence and test bullets might be impossible to match. Naturally the difficulty depends on the degree of fouling.

The „gilded" bullets (such as Lubaloy-coated) are in general more difficult to match than either the plain lead bullets or the jacketed ones. Plain lead bullets, as pointed out elsewhere, expand because of the pressure behind them and the frictional resistance produced by the walls of the barrel, and, consequently, they tend to fill the whole cross section of the barrel. This, together with the relative softness of the lead, causes the bullet to take good distinctive markings on both the lands and grooves. The „gilded" bullets, which present a somewhat harder surface, may not fill the whole cross section, at least not with the same pressure, and the markings may not be so well engraved on the bullet. Another difficulty arises due to „flaking" of the gilded surface, which presents a mottled appearance that interferes not only with the visual comparison but also with photography. The metal-jacketed bullets, having a harder surface, do not completely fill the cross section of the barrel. They may have excellent markings in the grooves but little or no markings on the lands. This disadvantage is offset by the fact that the engraved marks on a jacketed bullet are less susceptible to damage than those on the softer lead bullet.

Fig. 11. Comparison camera photos showing four matchings found on a pair of bullets fired from a .38 cal. S&W revolver.

Fig. 12. Unusual bullet-collecting medium. Lead bullets of .22 cal. were fired into a block of ice. Heat and pressure caused the ice to melt and little if any deformation occurred. The matchings shown (comparison camera) are better than those ordinarily obtained for .22 cal. lead bullets collected in the usual manner.

Fig. 13. Filar micrometer eyepiece. (Photo by courtesy of Bausch & Lomb.)

Fig. 14. Method of interchange. (Applied to photos in Fig. 26. ) Left: A portion of the photo of the Lowell Test Shell has been cut out and placed on the Evidence Shell. Right: A portion of the photo of the Evidence Shell has been placed on the upper part of the Lowell Test Shell.

Fig. 15. Matching by method of interchange.

No. 1. Photo of head of fatal shell. (Cut in half for interchange.) No. 2. Photo of head of test shell fired in suspect gun. No. 3. Upper half of photo No. 1 superimposed on lower half of photo No. 2. No. 4. Upper half of photo No. 2 superimposed on lower half of photo No. 1. This method, now considered obsolete, originated with the noted French criminologist Balthazard in 1912 when he applied it to the identification of fired bullets.

Fig. 16. Nose end of a .22 cal. lead bullet which had been fired through a wire window screen.

Fig. 17. Embedded fibers tell a story. During investigation of the murder of a hermit two bullets were found embedded in a wall, near each other. The bullets were of different caliber, and there was only one bullet hole through the body. Examination of the .35 cal. bullet disclosed blue cotton and white wool fibers embedded in the exposed lead of the nose end. Deceased had been wearing a blue denim jacket and a white wool undershirt. The .38 cal. lead bullet showed no such fibers but did show some mold in the cannelure indicating that it must have been fired at least several days previously.

Fig. 18. Remains of jacketed bullet. This portion of a soft-nosed jacketed bullet was taken from a body. No lead was recovered. The markings on the copper jacket served to identify the gun from which it had been fired.

Was this article helpful?

0 0
Knife Throwing Techniques of the Ninja

Knife Throwing Techniques of the Ninja

Knife Throwing Techniques of the Ninja. span stylecolor: 000000Do you want to learn the art of throwing knives? Ever wondered how it is done to perfection every time? Well here is your chance. This book contains well over 50 pages of detailed information and illustrations all about the art of knife throwing. This intriguing book focuses on the ninja's techniques and training. This is a must for all martial artists and anyone wanting to learn the knife throwing techniques of the ninja.span

Get My Free Ebook

Post a comment