Starline Unprimed Brass Cases 450 Bushmaster (50pk) - RN1. 693 1. 697 O. A. L. The 450 Bushmaster was designed as a close range, big bore hunting caliber for the AR 15 platform. As with most AR cartridge conversions, it only requires swapping out the upper receiver. With the introduction of some new bolt action rifles in this calibre and many states changing game laws allowing straight wall cartridges for deer hunting, the . 450 Bushmaster is enjoying a surge in popularity. Ruger now offers their American