Two things about mini-guns: they need their recoil springs replaced at a more frequent interval than full size guns and they may not operate reliably with +P ammo. This last has to do with the higher slide speed produced by the +P ammo.

The only way you're going to know about reliability is to try it over at least 100-200 rounds.

BTW, you cannot make up for lousy shot placement by increased velocity/caliber.