Method of making a bullet comprising a compacted mixture of copper powder
View Patent ↗A bullet comprising a compacted mixture of copper powder comprising particles that are physically bonded to each other to form a cohesive and ductile microstructure is disclosed. Methods of making such a bullet through powdered metallurgy techniques, which provide sufficient properties to allow the bullet to be loaded into a cartridge and crimped without fracture are also disclosed. Such bullets have sufficient strength to maintain their integrity during firing but may fragment upon impact and can be formulated lead-free.
1. A method of making a bullet comprising:
pressing a single metal powder comprising at least 98.5% by weight of copper in a mold to form a green compact; and
heating the green compact to a temperature that partially sinters the single metal powder to achieve physical bonding of copper particles and achieve a consolidated microstructure and to form a copper bullet comprising a cohesive microstructure, wherein heating the green compact is performed at a temperature ranging from 1300° F. to 1450° F.
2. The method of claim 1 , further comprises treating the surface of the copper bullet by performing at least one tumbling process.
3. The method of claim 1 , further comprising at least one step to introduce into the bullet at least one design chosen from a cannelure groove, a tipped point, a hollow point, boat-tail, ring, a grove, and combinations thereof.
4. The method of claim 1 , further comprising at least one post processing step to size the copper bullet to achieve a desired diameter.
5. The method of claim 1 , wherein the copper powder is pressed to a density ranging from 7.0 to 8.2 g/cc.
6. The method of claim 1 , wherein the green compact is heated to a temperature ranging from 1350° F. to 1450° F.
7. The method of claim 1 , wherein the green compact is heated to a temperature ranging from 1300° F. to 1400° F.
8. The method of claim 1 , further comprising adding at least one lubricant to the single metal powder prior to pressing.
9. The method of claim 8 , wherein said lubricant comprises molybdenum disulfide, lithium stearate, zinc stearate, carbon, synthetic wax, a polymer selected from polytetrafluoroethylene, polyethylene, polyamide, and polyvinyl alcohol, and combinations of any of the foregoing.
10. The method of claim 9 , wherein the synthetic wax comprises N,N′ Ethylene Bis-Stearamide or N,N′ Distearoylethylenediamine.