Now for the bad news (...Which is minor...)... Ya need the ejection port milled out a bit on your upper if ya use a regular AR upper, or ya can just buy a pre milled one from AERO, if ya can find one. Ya also need a 450 Bushmaster bolt as well. The bushmaster cartridge ...
In addition to Bushmaster, Ruger also produces their semi-automatic AR-556 in .450 Bushmaster. CVA produces their single shot Hunter and Scout rifles in the cartridge. The same goes for Savage and Ruger with their bolt-action 110, American Ranch, and Gunsite Scout rifles. SBR and Rock River...