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 caliber and many states changing game laws allowing straightwall cartridges for deer hunting, the .450 Bushmaster is enjoying a surge in popularity. This cartridge utilizes the common .452" diameter bullet, reloaders can use bullet weights anywhere from 160-350+ grains.