Sometimes the "backyard gunsmith" does not fully accomplish his goal of converting a semiautomatic weapon to fully automatic, resulting in a weapon that will occasionally fire in the fully automatic mode. Actual test-firing is often the only way to confirm this. The firearms examiner can load two or three rounds initially and attempt to get the weapon to fire multiple rounds with one pull of the trigger. If this is unsuccessful, a full magazine may be used. By examining the internal workings of the weapon the examiner can usually tell if there has been any attempt made to modify the weapon. Directions ammunition. According to records of the supplier, the suspect had received the ammunition several months prior to the murders. Perhaps most incriminating was an instruction sheet for a suppressor tube from a firearms accessory company.
The firearms examiner confirmed that in addition to the common shaved areas on the sides of each bullet were rifling marks consistent with a Ruger Mark II pistol. This did not mean that only a Ruger Mark II could have fired the bullets, but it did mean that a Ruger Mark II was among the possible weapons that could have fired them.
Based on his lying to investigators about being at the business the day of the shootings, his acknowledged dispute with the owner, and the circumstantial evidence to support that he acquired subsonic ammunition, a suppressor tube, and a Ruger 22 Mark II pistol, the man was convicted of first-degree murder. At trial his defense had pointed out that subsonic ammunition is available to anyone and is used for target shooting. Likewise, the Ruger Mark II pistol in 22-caliber is a common target pistol. With regard to the suppressor tube brochure it also included other products unrelated to suppressor manufacture. Furthermore, no confirmation of the defendant having ever actually purchased a suppressor or a suppressor tube was ever found. Obviously, the jury did not think there was reasonable doubt about it. What do you think?
for converting various weapons to fire fully automatic are available on the Internet.
Another modification that the firearms examiner may encounter is a sound suppressor. These are generally referred to as "silencers," although that is a misnomer. The only way to completely silence a firearm is not to fire it. Sound suppressors are only feasible with single shot, semiautomatic, or fully automatic weapons. Revolvers cannot be effectively suppressed due to the open space between the cylinder and the frame. The sources of sound involved in the discharge of a weapon are the expansion of hot gases from the powder and primer, the bullet breaking the sound barrier, and the action of the weapon (the hammer falling and slide moving back to reload). The latter two are most easily taken care of. The use of subsonic ammunition, that is bullets traveling slower than the speed of sound, eliminates the sonic boom associated with a supersonic bullet as it breaks the sound barrier. The action of the weapon can be locked so that it does not cycle.
The expanding hot gases create most of the noise associated with the discharge of a firearm. By slowing down the rate of expansion, the sound may be suppressed. Devices used for this purpose range from a two-liter plastic bottle placed over the gun muzzle to sophisticated metal expansion chambers containing baffles of various types and designs. These more sophisticated suppressors may be integral to the barrel or screw onto the end of the barrel.
In any event all that is required for there to be a violation of the National Firearms Act is for there to be any decrease in the audible report of the weapon. This may simply be determined by the examiner test-firing the weapon in question with and without the alleged suppressor and listening for a discernable decrease in the report. A more reliable method is to used a decibel meter to record the number of decibels produced with and without the device. This allows the examiner to establish a quantitative measure of the sound suppression. Again, even the slightest decrease in the audible sound constitutes a violation of federal law if the device has not been registered with the ATF. Thus, an aluminum soda can or a plastic bottle would conceivably have to be registered as a suppressor to be legally placed over the muzzle of a firearm.
The question of whether there is evidence of a weapon being fired can be answered conclusively in some instances. Many times the results of these examinations are inconclusive. The amount of time that has passed since the time of the shooting is a primary consideration. For example, if a shooting took place only a matter of hours or even days before and a suspect weapon is determined to have a barrel that is full of dust, corrosion, or other foreign material, it is extremely unlikely that the weapon was used in the shooting.
On the other hand, a thoroughly clean barrel cannot be taken as evidence of anything other than that the owner is meticulous about his or her weapon. Even finding a few gunpowder particles inside the barrel only allows an examiner to be able to say that there is evidence of firing since the last time the weapon was cleaned. In most instances there would be no way to conclusively determine when that time of last cleaning was.
When a revolver is fired, a pattern of soot is deposited around the margins of the chamber on the face of the revolver cylinder. The term halo or cylinder flare is used to identify these deposits, as shown in the photograph. This soot pattern can be correlated with the rotation direction of the cylinder, the chamber under the hammer, and the number of fired cartridge cases to help establish evidence of recent firing. For example, if only one shot was fired in a shooting incident and a revolver is suspected to be the responsible weapon, the presence of a single cylinder flare would be circumstantial evidence that this could be the responsible weapon.
Research is currently being done to use the vaporous residue present in gun barrels and fired cartridge cases to establish approximate time since firing. These residues persist for up to a day or longer, then totally dissipate. By determining the presence and quantity of these residues, researchers hope to be able to estimate reliably the time of shooting. This work may lead to a method that can be used to confirm what presently can only be speculated.
As has been previously described, the firearms examiner's most common task is to determine whether bullets, cartridge cases, and shot shells have been fired in weapons either found at crime scenes or recovered from suspects. To do this the firearms examiner must obtain ammunition similar to that in question. The reason for this is that differences in the hardness of bullets and cartridge case brass can result in differences in the markings left by firearms. For example, lead bullets and copper jacketed bullets (that is, bullets consisting of an inner core of lead with
an outer skin of copper) acquire significantly different markings. Primer case composition can also vary, and some primer cases are much harder than others. This can also result in significantly different marks from the same firing pins and breech faces. As in any scientifically based test, the examiner must duplicate the actual event as closely as possible in order to be able to produce any meaningful results.
The firearms examiner will typically fire a minimum of three test rounds from the suspect weapon. The water trap is used to stop the bullets and minimize their distortion and alteration of surface markings from the interior of the gun barrel. Even with water, however, highvelocity bullets can distort and even disintegrate upon impact with the surface. Anyone who has done a belly flop into water knows that water is really not that soft! The firearms examiner must sometimes reduce the powder charge in a cartridge in order to slow the bullet enough to keep it from distorting or disintegrating. To do this the examiner refers to charts found in reloading manuals for "reduced loads" and manually reduces the powder charge of a commercially produced cartridge.
First the examiner removes the bullet using a tool known as an inertia bullet puller. This resembles a plastic mallet with a hollow head. The
cartridge is placed into a special collet (holder) that holds it in the hollow space. The puller is then struck against a hard surface with a swinging motion, like one would strike a blow with a hammer. The inertia of the bullet causes it to dislodge from the case while the collet holds the cartridge case in place. The examiner removes the powder, weights out a lesser portion, places it back into the cartridge case, then manually reinserts the bullet into the cartridge case. The reduced load is now ready to be fired.
A potential problem with firing reduced loads is that the cartridge case may not receive markings from the chamber, breech face, and firing pin that are as prominent as those from a full powder charge. This is because less powder results in less force of expansion. With lead bullets, however, less powder can actually result in better retention of barrel markings, since the hot gases associated with a full powder charge have a tendency to erode the soft lead. Copper jacketed bullets do not exhibit this effect.
Diagram of striations as viewed through a microscope
Once the examiner has collected the fired bullets and cartridge cases, the task of comparing microscopic markings on bullets and cartridge cases begins. This involves mounting two bullets or two cartridge cases on the comparison microscope, one on each side or stage, and carefully observing as one is slowly rotated while the other remains fixed. The idea is to find that particular area where the microscopic markings are of sufficient quality and quantity to call it a match. The figure illustrates the type of markings that the examiner looks for.
To answer the last of the questions posed in this section, the muzzle-to-target distance in a shooting incident, the firearms examiner may use several different approaches depending on the type of weapon involved. For shots from any type weapon the firearms examiner will first look for the presence of gunpowder particles on skin and/or clothing. The general rule of thumb is that gunpowder will be expected to strike the target if the shot was fired within arm's length or less. When a firearm is discharged, gunpowder particles exit the muzzle in a conical distribution. The farther away the target is from the muzzle of the gun, the greater the gunpowder pattern diameter will be, as illustrated in the diagram.
Exactly how far the gunpowder particle will travel horizontally depends on three things: particle shape, gravity, and air friction. Gunpowder for handguns comes in three different shapes known as ball, flattened ball, and flake or disk. To determine which gunpowder particle shape would travel the farthest, given the same initial velocity, one need only imagine trying to throw a soccer ball versus trying to throw a dish or plate baseball style. The aerodynamic shape of the ball powder (spherical) allows it to easily outdistance the other shapes.
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Conical distribution of gunpowder particles
Ball Flattened ball Flake
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Gunpowder shapes (as emitted from a handgun)
Like that for handguns, gunpowder designed for use in rifle cartridges also comes in ball, flattened ball, and flake or disk, but tubular powder particles are available as well. The reason for the different powder particle shapes, or morphologies, has to do with differences in burning rates. Gunpowder may consist of nitrocellulose or a combination of nitrocellulose and nitroglycerin (so-called single-base and double-base powder). There is actually quite a lot of physics involved in the design of a cartridge. The reason is the differences in ballistic requirements: different barrel lengths, calibers, bullet weights, and bullet designs require specific loads for optimum performance. Shotgun shells (shot shells) involve similar considerations.
In order to be sure that cartridges can be successfully and safely fired from all sorts of different weapons under a wide variety of atmospheric conditions, manufacturers put more than enough powder in
The ability of ball powder to outdistance other gunpowder shapes is not only a consideration for powder particles traveling through the air but also through bodies and other dense material. In his textbook Gunshot Wound, Vincent Dimaio notes that he has encountered cases in which victims were shot through the head at contact or near contact range, and ball powder actually passed through the skull with the bullet.
In another case familiar to this author, a very obese man was shot in the side at contact range with a 357 magnum loaded with ammunition containing ball powder. The bullet exited the man's body on the opposite side. An examination of the man's wound at autopsy revealed gunpowder particles inside the wound tract. Examination of the man's shirt revealed no gunpowder around the entrance hole but a considerable amount of gunpowder on the inside of the shirt around the exit hole. The ball powder had traveled completely through this large man's body!
The author examined a case involving an errant shot in a drive-by shooting that struck and killed a young girl who happened to be standing in the wrong place at the wrong time. Who fired the fatal shot was in dispute. The bullet passed through the victim and was never recovered, so there was no way to identify the shooter's gun. Because two particles of ball powder were found on her clothing, it was proposed that the shot had to come from the man standing in the yard within eight feet (2.4 m) of her and not from the individual who was firing from the vehicle approximately 1 5 feet (4.6 m) away. An unrelated study conducted by Dimaio, however, showed that individual particles of ball powder fired from a 38-caliber revolver could travel as far as 20 feet (6.1 m). Thus, the shot could have come from the vehicle. Since no one knew which way the little girl had been facing when she was shot and both shooters were firing 38 revolvers with ball powder, it was not possible to rule out either.
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