Ream it to 460 s&w. Mine is still accurate with 45 colts in the 460 chamber. You can shoot 45 ACP, 45 WinMag (w/Orings for headspace), 45 Cowboy, 45 Schofield, 45 Colt, 454 Casull, and 460 S&W. Haven't tried 45 GAP but it should work if the rim is close to 45 ACP size. I have shot up to 525 gr out of the 460. With plastic stock and no weight in the butt, it will probably get your attention within a few shots with full bore loads. With the 45 Cowboy (rimmed 45ACP) it is quiet and kickless. Mine is fond of 480 gr Lyman in 45 Colt cases with an undisclosed charge of Lil Gun (no published data).