The .450 Bushmaster is a rifle cartridge developed by Tim LeGendre of LeMag Firearms, and licensed to Bushmaster Firearms International. The .450 Bushmaster is designed to be used in standard M16s and AR-15s, using modified magazines and upper receiver assemblies.
The .450 Bushmaster makes use of .452 in. bullets because the lower impact velocities and energies would not adequately expand the heavier jacketed .458 in. bullets. The cartridge is chambered in bolt-action rifles by Ruger, Savage, Mossberg, and Remington, Ruger's No. 1 single shot rifle, AR-15 rifles, as well as an AR-15 pistol by Franklin Armory.
Ballistically, the .450 Bushmaster has a rather flat trajectory out to 200 yards; if the firearm is zeroed at 150 yards, the user can expect to see a rise of 1.8 inches at 100 yards, zero at 150 yards, and a drop of 4.9 inches at 200 yards. The cartridge fits single-stacked in a standard AR-15 magazine with a single-stack follower. A 10-round AR-15 magazine body yields a four-round magazine, a 20-round AR-15 magazine body yields a five- to seven-round magazine, and a 30-round body yields a nine-round magazine. Hornady, Remington and Federal now manufacture ammunition for the rifle, and Starline manufactures empty brass for handloading.