My MKii like Bo's has trouble cycling the better quality lower velocity subsonic and target ammo. Suppressed, it cycles then very well. Standard and high velocity it cycles fine. Obviously, get the best accuracy out of the subsonics. Its a tack driver!! Remington makes a decent subsonic hollow point ammo that WILL cycle just fine unsupressed. Not quite as accurate as the some of the better Eley, and RWS subsonic hollow points. But its a lot cheaper and still shoots good enough to kill squirrels.