Frangible firearm projectiles, methods for forming the same, and firearm cartridges containing the same

Abstract

Frangible firearm projectiles, firearm cartridges, and methods for forming the same. The projectiles are formed from metal powder and include an anti-sparking agent. One or more of iron, zinc, bismuth, tin, copper, nickel, tungsten, boron, and/or alloys thereof may form the metal powder. The projectiles may be formed from a compacted mixture of two or more different metal powders. The anti-sparking agent may include a borate, such as boric acid, zinc chloride, and/or petrolatum. The anti-sparking agent may be dispersed within, and/or applied as a coating on, the exterior of the projectile. The compacted mixture may be heat treated for a time sufficient to form a plurality of discrete alloy domains within the compacted mixture. Such domains may be formed by a mechanism that includes vapor-phase diffusion bonding and oxidation of the metal powders and that does form a liquid phase of the metal powder or utilize a polymeric binder.

1 . A frangible firearm projectile, comprising:
 a frangible projectile body consisting essentially of a compacted mixture of metal powders that forms at least 90 wt % of the frangible projectile body; and   wherein the frangible firearm projectile includes an anti-sparking agent configured to reduce a propensity for the frangible firearm projectile to produce sparks upon striking a target after being fired; and further wherein the anti-sparking agent includes at least one of boric acid, borax, and a borate.   
     
     
         2 . The frangible firearm projectile of  claim 1 , wherein the anti-sparking agent is boric acid. 
     
     
         3 . The frangible firearm projectile of  claim 1 , wherein the anti-sparking agent is interspersed within an interior of the frangible projectile body. 
     
     
         4 . The frangible firearm projectile of  claim 1 , wherein the anti-sparking agent forms at least a portion of a coating on an exterior of the frangible projectile body. 
     
     
         5 . The frangible firearm projectile of  claim 1 , wherein the anti-sparking agent further includes zinc chloride, petrolatum sodium bicarbonate, polybenzimidazole fiber, melamine, modacrylic fiber, and hydroquinonone. 
     
     
         6 . The frangible firearm projectile of  claim 1 , wherein the anti-sparking agent forms 0.5-5 wt % of the frangible firearm projectile. 
     
     
         7 . The frangible firearm projectile of  claim 1 , wherein the compacted mixture of metal powders includes metal powder of at least one of zinc, iron, copper, tungsten, bismuth, nickel, tin, boron, and alloys thereof. 
     
     
         8 . The frangible firearm projectile of  claim 1 , wherein the compacted mixture of metal powders includes iron powder and zinc powder. 
     
     
         9 . The frangible firearm projectile of  claim 8 , wherein the iron powder forms a majority component of the compacted mixture, by weight. 
     
     
         10 . The frangible firearm projectile of  claim 8 , wherein the compacted mixture includes at least 5 wt % zinc powder. 
     
     
         11 . The frangible firearm projectile of  claim 1 , wherein the compacted mixture of metal powders includes copper powder. 
     
     
         12 . The frangible firearm projectile of  claim 11 , wherein the compacted mixture of metal powders includes at least 60 wt % copper powder. 
     
     
         13 . The frangible firearm projectile of  claim 1 , wherein the frangible firearm projectile has a density of at least 6.5 grams per cubic centimeter. 
     
     
         14 . The frangible firearm projectile of  claim 1 , wherein the compacted mixture of metal powders includes 80-90 wt % iron powder and 10-20 wt % zinc powder, wherein the frangible firearm projectile has a density of at least 6.5 grams per cubic centimeter, wherein the frangible firearm projectile has a weight and is configured to break entirely into small particulate when fired at a metal surface at close range from a firearm cartridge, and wherein the small particulate has a maximum particle weight of 5% of the weight of the frangible firearm projectile. 
     
     
         15 . A firearm cartridge, comprising:
 a casing that defines an internal volume;   a propellant disposed in the internal volume;   a primer disposed in the internal volume and configured to ignite the propellant; and   the frangible firearm projectile of  claim 1  at least partially received in the casing.   
     
     
         16 . A method for forming the frangible firearm projectile of  claim 1 , the method comprising:
 preparing a mixture of metal powders and the anti-sparking agent;   compacting the mixture of metal powders and the anti-sparking agent to form a compacted mixture;   heating the compacted mixture to a heating set point temperature; wherein the heating set point temperature is at least 260° C. (500° F.) and less than 404.4° C. (760° F.);   maintaining the compacted mixture at a maintaining temperature for a maintaining time; wherein the maintaining time is at least 20 minutes, wherein the maintaining temperature is within 10% of the heating set point temperature; wherein the heating and the maintaining create a plurality of discrete alloy domains of the iron powder and the zinc powder within the compacted mixture; and   cooling the frangible firearm projectile.   
     
     
         17 . The method of  claim 16 , wherein the heating includes a heating phase that includes increasing the temperature of the compacted mixture at a heating rate that is in the range of 1-5° C./minute, and further wherein the heating does not include melting any of the metal powders in the compacted mixture; and further wherein the method does not include adding a polymeric binder to the mixture of metal powders. 
     
     
         18 . The method of  claim 16 , wherein the cooling includes cooling the compacted mixture at a cooling rate in the range of 1-5° C./minute to a cooling set point temperature that is less than 250° C. and greater than 150° C. 
     
     
         19 . The method of  claim 16 , wherein the compacting includes compacting the mixture of metal powders to at least 50,000 pounds per square inch (psi) (344.8 megapascal (MPA)). 
     
     
         20 . A method of assembling a firearm cartridge, the method comprising:
 forming at least one frangible firearm projectile by the method of  claim 16 , and   loading the at least one frangible firearm projectile into a casing that includes a propellant and a primer configured to ignite the propellant.   
     
     
         21 . A firearm cartridge formed by the method of  claim 20 , wherein the frangible firearm projectile has a density of at least 6.5 g/cc and a weight, and wherein the frangible firearm projectile is configured to break entirely into small particulate having a maximum particle weight of 5% of the weight of the frangible firearm projectile when fired at a metal surface at close range from a firearm cartridge.