I have a spare Savage Stagger Feed short action and would like to build a 458 socom or 450 Bushmaster just to play with. I was wondering if there is anyway of having a reliable repeater with any of these cartridges in a stagger feed action. I am mainly wanting to build something subsonic to play with, but would like a repeater. I have heard of extraction issues with the 300 Whisper, and have also considered the 338BR. Any advice on a reliable round for a repeater would be appreciated.