6mm Lee Navy

The 6mm Lee Navy (6×60mmSR), also known as the 6mm U.S.N. or .236 Navy, is an obsolete American rifle cartridge. It was the service cartridge of the United States Navy and Marine Corps from 1895, officially replacing the .45-70 Government round, and was the first small-bore high-velocity smokeless powder cartridge to be adopted by either service. The 6mm Lee Navy was in turn replaced by the .30 Army (.30-40 Krag) cartridge in 1899.

History and development

By 1894, the U.S. Navy desired to adopt a modern small-bore, smokeless powder service cartridge and rifle in keeping with other first-line naval powers for both naval and marine forces. Naval authorities decided that the new cartridge should be adaptable to both rifles and machine guns. Noting that the world's military forces were adopting smaller and smaller caliber rifles with higher velocity cartridges, U.S. naval authorities decided to leapfrog the trend to smaller and smaller calibers by adopting a cartridge in 6 mm (0.236 inch) caliber, with a semi-rimmed case capable of holding up to 40 gr (0.091 oz; 2.6 g) of 'rifleite' smokeless powder and proof chamber pressures of up to 60,000 psi. While the government cartridge was being developed, the Navy tested rifle barrels in various alloys and rifling twists, eventually settling on a barrel steel made of 4.5 percent nickel steel, with a rifling twist of one turn in 6.5 inches.