RSM's have used to rechamber to 450 Rigby and 470 Mbogo. All are based on the 416 brass. All it takes is a re-barrel job. I used think of maybe re-boring but can't take the year or so wait for it to come back. The 450 has a 500 gr. going out at 2400-2500 if you can stand the recoil. The 470 has been used with a 500-600 gr going out from 2200 to 2500. OUCH!