If a weapon has been recovered, it will be necessary to compare fired ammunition from this weapon with fired ammunition recovered from the scene.
Obtaining a series of test cartridge cases from a self-loading pistol presents little difficulty as they merely have to be picked up. Obtaining fired bullets in a near pristine condition is, however, a little more difficult.
In the past, cotton waste or wadding has been used, but this material can be quite abrasive to soft-lead bullets especially those of 0.22" rimfire calibre.
High grade, long-fibre cotton wool is extremely good at preserving the finest stria on the softest of lead bullets. It is, however, very expensive and has to be frequently replaced.
Vertical and horizontal water tanks for bullet recovery are currently very popular, but these also have their own problems.
One of the major problems faced with all water recovery tanks is that of algae formation. The nitrates in gunshot residues form an ideal breeding ground for algae and the tank soon becomes a thick green soup. Whilst this does not effect the bullet recovery, it is not a pleasant medium to work with. Bleach or a bactericide can be used to remove this algae, but great care must be taken to ensure that the bullet surface is not corroded by whatever is added to the water.
Horizontal bullet recovery tanks, where the bullet is fired at an angle from one end into the top of the tank, suffer from bullet recovery problems. Once the bullet loses its velocity, it drops to the bottom of the tank and the only practical way of recovering it is with a piece of Plasticine or Blue -tak on the end of a long stick. Locating the bullet is another problem as the formation of algae can make it very difficult to find the bullet in the first place.
In addition, the firer has to be extremely careful that the bullet does not ricochet from the water's surface. Too steep an angle and the bullet will penetrate the bottom of the tank, too shallow, and it will ricochet.
The tanks, when full of water, are also extremely heavy, often requiring floor reinforcement and, as they are generally made from sheet stainless steel, very expensive.
Vertical bullet recovery tanks do not suffer with ricochet problems, but they do have to be a minimum of 6 ft deep to ensure that the bullet loses all its veloc ity before reaching the bottom of the tank. With a minimum depth of 6 ft, the tank is often sited on one floor of a building with the base resting on the floor below.
One problem which all water recovery tanks suffer from is the propensity for the bullet to spiral down the tank, eventually hitting the sides and becoming damaged. This problem is, for some unknown reason, particularly acute with vertical tanks.
This problem is commonly referred to as bullet progression and appears to be a function of bullet yaw in which the bullet prescribes a spiral round the axis of its flight. This is due to over-stabilization of the bullet by the rifling, much as in the wobbling motion of a top when it is first spun.
This spiral round its flight axis is accentuated by the increased density of water over air which sends the bullet into an ever-increasing spiral as it progresses down the tank. If the tank is not of sufficient diameter, the bullet will contact the sides of the tank and become badly damaged. A vertical tank diameter of 3 ft (1 m) is considered the absolute minimum.
Another problem with vertical recovery tanks is the hydraulic shock produced when a bullet is fired into water. As water is non-compressible, a shock wave is produced when it is struck by a bullet. This shock wave travels down the tank, bulging the walls quite alarmingly. When the tank regains its original shape, it rebounds, lifting it off its base and sending large quantities of water out of the top of the tank. The continual hammering action of the tank jumping off its base (even though this might be just a fraction of an inch) and the bulging of its sides can have quite serious consequences for the building in which it is sited.
In one instance, a very large tank was sited in the corner of a forensic laboratory building. After several hundred rounds of ammunition had been fired into it, the bulging sides and hammering action on its base had pushed out the walls of the building to such an extent that there was a 6 in. gap straight through the brickwork on either side.
Probably one of the most convenient and cheap materials for bullet recovery goes under the trade name of 'Crocell (Crocell Hot Dip)'. This is a high molecular weight petroleum jelly which is used as a protective coat on high- quality engineering tools. The material, which comes in granulated form, is simply melted then cast into 1 in. (25 mm) thick slabs which are placed into a long wooden or steel box. Bullets fired into this material stop in a surprisingly short space (12 in. for a 0.38" Special and 20 in. for a 9 mm PB) and can be recovered quite easily by pulling out the sheets.
The material is exceedingly good at preserving fine stria even for the softest of lead bullets. In addition, after 30 or so shots, the damaged sheets are merely recast.
Care should be taken to ensure that during firing, a piece of card is placed in front of the first sheet of Crocell. If this is not done, unburnt propellant particles which issue from the muzzle of the weapon will accumulate in and on the front sheet of Crocell. After a few recastings, the quantity of propellant in the Crocell can reach levels where a distinct fire hazard will exist.
Probably one of the most unusual cases involving bullet recovery resulted from the strafing of a fishing boat by a military aircraft. The boat was not sunk but was badly damaged. Upon examination of the boat, two 30 mm cannon bullets were found lodged in the smashed engine block and mountings. A microscopic examination of the copper driving bands on the bullets showed that they had been fired through different barrels. Eventually, a number of aircraft were located which could have carried out the shooting, each of which was armed with four 30 mm cannons.
Obviously, Crocell and cotton wool were not going to be the first choice of recovery materials for this type of missile. In the end, a 200 ft trench was dug, which was 6 ft wide and 6 ft deep. Into a pit at one end of the trench was mounted an action from a 30 mm cannon onto which the barrels from the suspect aircraft could be attached one at a time. The pit was filled up with sawdust, which was then soaked in oil. A soldier was positioned every 10 ft along the pit and as the disturbance from the cannon bullet passing through the sawdust was seen, he raised his arm. The last soldier to raise his arm was then given a shovel and told to dig! After much noise and hours of digging, sufficient bullets were located, which were used to determine whose guns were used to strafe the ship.
Was this article helpful?