Lead projectiles and lead shot expended at shooting ranges pose a significant environmental hazard. Disposal of the lead contaminated sand used as a backstop in indoor ranges is expensive, since lead is a hazardous material. Due to the low value of lead metal, reclamation of the lead from the sand is not economically feasible for most target ranges. At outdoor ranges, the lead must be removed before the range land can be used for other purposes. Frequently, the entire top soil layer is removed and disposed elsewhere, a time consuming and costly operation.

 

 

Accordingly, there exists a need for an effective lead free bullet that is easily separated from range soil and sand.

 

Density differences between bullets of the same size result in differences in long range trajectory and differences in firearm recoil. Such differences are undesirable. The shooter needs to have a consistent trajectory and a recoil so the "feel" of shooting a lead free practice round should be similar to that of shooting a lead service round. If there are differences in trajectory and recoil, experience gained on the practice range will degrade, rather than improve, accuracy when firing a lead bullet in the field.

 

Accordingly, it is an object of the invention to provide a projectile that is substantially lead free. A second object of the invention is for the projectile to have ballistic performance similar to lead. A third object of the invention is for the projectile to be easily removed from the shooting range soils and backstops.

 

It is a feature of the invention that the projectile is a sintered composite having one or more, high density constituents selected from the group consisting of tungsten carbide, tungsten, ferrotungsten, cemented tungsten carbide alloys and carboloy (a tungsten carbide-cobalt sintered alloy, typically containing from 3% to 13% by weight cobalt), and a second, lower density constituent selected to be a metallic matrix material such as tin, zinc, iron, nickel, cobalt and copper. Alternatively, the second constituent is a plastic matrix material such as a phenolic, epoxy, dialkylphthalate, acrylic, polystyrene, polyethylene, or polyurethane. It is another feature of the invention that an effective amount, typically more than 50% by weight, of the projectile constituents are ferromagnetic. In addition, the composite projectile may contain a filler metal such as iron powder or zinc powder. The bullet of the invention comprises a solid body having a density of at least about 9 grams per cubic centimeter (80 percent that of pure lead) and a yield strength in compression greater than about 4500 psi.

 

Other constituents may be added in small amounts for special purposes such as enhancing frangibility. If iron is one constituent, the addition of carbon results in a brittle microstructure after a suitable heat treatment. Lubricants or solvents can be added to enhance powder flow properties, compaction properties and ease die release.

 

It is an advantage of the invention that ferrotungsten is ferromagnetic and has a density greater than that of lead. A ferrotungsten containing composite is economically feasible for projectiles and, by metallurgical and ballistic analysis, can be alloyed in proper amounts under proper conditions to become useful for a lead free bullet.

 

The invention further stems from the realization that ballistic performance can best be measured by actual shooting experiences since the extremes of acceleration, pressure, temperature, frictional forces, centrifugal acceleration and deceleration forces, impact forces both axially and laterally, and performance against barriers typical of bullet stops in current usage impose an extremely complex set of requirements on a bullet that make accurate theoretical prediction virtually impossible.

 

There are at least six requirements for a successful lead free bullet. First, the bullet must closely approximate the recoil of a lead bullet when fired so that the shooter feels as though he is firing a standard lead bullet. Second, the bullet must closely approximate the trajectory, i.e. exterior ballistics, of a lead bullet of the same caliber and weight so that the practice shooting is directly relevant to shooting in the field with an actual lead bullet. Third, the bullet must not penetrate or damage the normal steel plate backstop on the target range and must not ricochet significantly. Fourth, the bullet must remain intact during its travel through the gun barrel and while in flight. Fifth, the bullet must not damage the gun barrel. Sixth, the cost of the bullet must be reasonably comparable to other alternatives.

 

Plastic Matrix

Frangible plastic matrix composite bullets were made of tungsten powder with an average particle size of 6 microns. Iron powder was added to the tungsten powder at levels of 0, 15, and 30 percent by weight. After blending with one of two polymer powders, phenyl formaldehyde (Lucite) or polymethylmethacrylate (Bakelite) which acted as the matrix, the mixtures were hot compacted at a temperature within the range of from about 300° F. to about 350° F. and a pressure of about 35-40 ksi into 1.25 inch diameter cylinders which were then cut into rectangular parallelepipeds for compression testing and drop weight testing.