.45 ACP bolt-gun suppressed. Cool! That would be fun - and takes .45 Auto mags as well. Years ago (80's), I had some 11 round mags when I played at IPSC - they'd be super - but I don't remember their make.
With the angle of the magazine putting the bullets right at the chamber's mouth, I suspect bolt throw was shortened to an inch and a bit, as well. Capable of being a VERY fast firing bolt gun with no recoil to speak of.