Lead free frangible iron bullets

Abstract

The invention relates to sintered iron bullets having increased frangibility (or which can be easily fragmented) and to the materials and processes for the manufacture of such bullets. The bullets of the present invention are typically made from iron powder (including powdered iron from scrap iron) which are pressed to form a briquette and then sintered under conditions so as to obtain bullets with the desired level of frangibility. In the preferred embodiment of the invention, the bullets are resin or plastic impregnated and then coated to facilitate lubricity and prevent corrosion.

What is claimed: 
     
         1 . A frangible bullet comprising at least 95% by weight iron and manufactured by pressing an iron containing powder in a die to form a briquette and subsequently sintering said pressed power compact, wherein said sintering:
 a. includes the addition of lubricants to aid in the briquetting process said lubricants comprising a mixture of range of generally from about 0.3% to about 1.0%, wt % lubricant, typically Zinc Stearate;   b. includes a lubrous coating and the coating ranges generally less than 1% by weight, often no significant weight increase with the phosphate coating; and   c. controls the density of said briquette in a range of generally from about 6.2 grams/cc to about 7.0 grams/cc, Through control of sintering temperature, or sintering time, or any combination of the above in a range of generally from about 1000° F. to about 1800° F., so as to produce a bullet capable of fragmenting upon impact with a steel target or other similar hard surface.   
     
     
         2 . The bullet of  claim 1  wherein said lubricants are from about 0.6 to 0.8% by wt lubricant the briquette has a density of 6.6 to about 6.8 grams/cc. 
     
     
         3 . The bullet of  claim 1  wherein the bullet is sintered at a temperature of from about 1400° F. to about 1500° F. 
     
     
         4 . The bullet of  claim 1  wherein the final composition is substantially lead-free. 
     
     
         5 . The bullet of  claim 1  wherein said bullet is comprised substantially of sintered of iron powder 
     
     
         6 . The bullet of  claim 1  wherein resin or plastic materials of from about 0.02 grams to about 0.05 grams are impregnated into the briquette to aid in the coating processes. 
     
     
         7 . The bullet of  claim 1 , further comprising a phosphate coating to enhance lubricity. 
     
     
         8 . The bullet in  claim 1 , further comprising a copper plating coating to enhance lubricity. 
     
     
         9 . The bullet of  claim 1  where in the bullet is plated with coating phosphate, copper and alloys and mixtures thereof. 
     
     
         10 . The bullet of  claim 9  further comprising loading of the bullet into a shell casing with propellant for producing a fireable cartridge. 
     
     
         11 . The bullet of  claim 9 , wherein the briquette occurs with an additive that acts as a briquetting agent lubricant. 
     
     
         12 . The bullet of  claim 9 , wherein the coating is effective for keeping the bullet lubricated for firing down the barrel of a gun. 
     
     
         13 . The bullet of  claim 1  wherein the briquetting and sintering controls;
 a. The density of said pressed powder compact to be in the range of 6.2-7.0 grams/cc; and 
 b. The frangibility of the pressed powder, such that it does not break up in the barrel of a gun. 
 
     
     
         14 . A method of making a frangible bullet which comprises pressing a powder containing at least 95 percent by weight iron, or iron alloy, or iron alloy powder, in a die to form a pressed powder compact and subsequently sintering said pressed powder compact, wherein briquetting and sintering forms a projectile which includes;
 a. frangibility as measured from the largest size of fragment of generally from about 1.1% to about 15% of said powder; and   b. density of generally from about 6.2 grams/cc to about 7.0 grams/cc.   
     
     
         15 . A method of  claim 14  wherein the pressing of the powder is performed at a pressure ranging from 20 to 50 psi. 
     
     
         16 . A method of  claim 14  wherein the sintering is performed in a protective atmosphere at a temperature ranging from 1200 degrees F. to 2100 degrees F. for a length of time from about 10 minutes to about 4 hours. 
     
     
         17 . The method of  claim 14  wherein the bullet has a largest size of fragmentation of from about 10 to 13%. 
     
     
         18 . The method of  claim 14  wherein the bullet has a largest size of fragmentation of less than about 10%. 
     
     
         19 . The method of  claim 14  wherein the density of the bullet is from about 6.6 grams/cc to about 6.8 grams/cc of said powder