i shoot a .303 magnum, i love the gun. its a .303 blown out and necked down from .312 to 308 so you can fire any old 30 cal bullet out of it. you cant ream out your existing chamber to the .303 kanuk magnum like mine but you can ream the chamber out for .303 epps, which is also a nice bullet if you are a die hard .31 cal fan or you want to shoot larger bullets more accurate