Ammunition and explosives – Cartridges
Reexamination Certificate
2000-07-17
2001-07-24
Mai, Ngoclan (Department: 1742)
Ammunition and explosives
Cartridges
C102S517000, C075S246000
Reexamination Certificate
active
06263798
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to frangible metal articles, and, in particular, to frangible bullets having particular use in target and/or training applications. Indoor and outdoor shooting applications benefit from the absence of lead as well as the frangibility (break-up) characteristics. Frangible bullets for such uses are well known. They are characterized by the use of metal powder consolidated into a bullet that has sufficient strength to maintain its integrity during firing while fragmenting on impact with a solid object having sufficient mass and rigidity to fracture the bullet.
Conventional, full-density, cast, swaged, copper plated or copper jacketed lead bullets are also used in indoor firing ranges and for training. In order to protect the shooters from ricochets, a “bullet trap” is normally required to stop the projectile and any resulting fragments from injuring shooters. Furthermore, the walls of the firing range or training facility may be covered with rubber or some other projectile absorbing material to stop occasional ricocheting bullet fragments. Thus, the cost of constructing and maintaining indoor target/training ranges is substantial. Moreover, even using bullet traps and ricochet absorbing materials on the walls, occasionally a ricochet will somehow defeat such systems and injure a shooter.
Shooting lead bullets causes the emission of airborne lead dust that is introduced into the atmosphere. This requires the implementation of elaborate ventilation systems and may require individuals working in such facilities to undergo blood monitoring programs to determine the amount of lead in their bloodstream. The accumulation of spent lead bullets and bullet fragments must be properly disposed of and regulations concerning the disposal of lead waste are becoming increasingly complex. Thus, the generation of lead dust and the accumulation of spent lead bullets and fragments causes environmental concerns and poses the potential for serious health problems.
There has been a long-standing search for a material to use as a bullet that does not contain lead. One problem in replacing lead in ammunition is that the replacement material must be sufficiently heavy such that ammunition using such bullets, when used in automatic or semi-automatic weapons, will be able to cycle the weapon properly.
The main criteria for the ability of a round to cycle automatic or semi-automatic weapons is the amount of energy that the ammunition delivers to the cycling mechanism. For some types of weapons, this energy is delivered by the expanding gases pushing back the cartridge case. For some others, the recoil is used and for still others high-pressure gases are connected, through a port inside the barrel, to a mechanism that cycles the firearm.
All firearms, are designed to function with bullets and propellants (gunpowder) that produce certain pressure-vs-time characteristics. Using a lighter bullet may cause problems in operation of a semi-automatic or automatic weapon if there is too low an energy transfer to give the mechanism the needed energy to cycle. While the energy can be increased by the use of additional propellant or different types of propellants, this is not desirable because the characteristics of such a training round would be significantly different from the ammunition having conventional bullets and propellants.
In addition, in order to replace lead in a bullet, the selected material should have a large enough specific gravity so that the resulting bullet mass is compatible with commercially available propellants. It is not economically feasible to develop a lead-free round where a special propellant or other component would need to be developed.
Further, a lead-free, training round should break up into small particles when it hits a hard surface. The individual particles are then too light to carry enough energy to be dangerous. On the other hand, such bullets should be sufficiently strong to withstand the high accelerations that occur on firing, ductile enough to engage the barrel rifling and durable enough to retain the identifying engraving from the rifling as required by government agencies.
Practice and training rounds employing combinations of resinous binders and metallic powders have generally not proven satisfactory because of uncontrollable frangibility characteristics, insufficient strength, increased fouling of the barrel of the weapon, decreased barrel longevity and inability to retain or receive engraving from the rifling of the barrel through which it is fired.
SUMMARY OF THE INVENTION
Accordingly, the present invention is directed to a frangible metal bullet, and a method of making same, which substantially obviates one or more of the limitations and disadvantages of the prior art.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the article and method particularly pointed out in the written description and claims thereof as well as the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the invention, as embodied and broadly described, the present invention is directed to a frangible metal bullet and a method for making it. The bullet comprises a plurality of metal particles and a brittle binder. Preferably the brittle binder consists essentially of at least one intermetallic compound formed from the metal particle and a binder material. The binder material is a metal or metalloid that forms a brittle binder at a treatment temperature below the temperature of joining of the metal particles, below the temperature of formation of substantial amounts of a ductile alloy of the metal of the metal particles and the binder material and above the temperature at which the binder material and the metal particles form at least one intermetallic compound that joins the metal particles into a coherent, frangible article. According to the method of making the article, the metal particles and powdered binder material are compacted to the shape of the metal article, then heated to the treatment temperature for a time sufficient to form at least one intermetallic compound, and then cooled to form the frangible metal bullet.
In further aspects of the invention, the metal particles are metals or metal-base alloys selected from copper, iron, nickel, gold, silver, lead, chromium and their alloys; and preferably copper or copper-based alloys, and the binder material consists essentially of materials selected from tin, zinc, gallium, germanium, silicon, arsenic, aluminum, indium, antimony, lead, bismuth, and their alloys and preferably tin or tin-based alloys.
Another embodiment is a frangible metal bullet comprised of a plurality of unsintered metal particles and at least one intermetallic compound binder joining the metal particles to form the metal bullet.
In further aspects of this embodiment, the binder has a microstructure of a porous, brittle material and the final treated product using such a binder has a transverse rupture strength of less than 13,000 psi. Frangible bullets having such properties are fractured into a plurality of particles by brittle failure of the binder, such that the fracture absorbs the majority of the kinetic energy of the bullet.
In still a further embodiment, the invention is a method of making a frangible, metal bullet, comprising the steps of: forming a mixture comprising metal particles, for example, copper and copper alloys and a metal binder material, the metal binder material comprising metals and alloys, disposed to form intermetallic compounds with the metal of the metal particles, for example, tin and tin alloys. The mixture composition is disposed to form a brittle binder at a treatment temperature below the temperature of joining of the metal particles, below the temperature of formation of substantial amounts of a ductile a
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Mai Ngoclan
SinterFire Inc.
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