Don't press up on the mag when you are shooting keep your fingers off it just don't touch it, I don't think this would cause the failure to return to battery but its worth a shot, and this may sound strange but are you using a push pull method with your grip push with the web of your right hand pull with the bottom of your left, try to let it recoil straight back, not muzzle up let your elbows bend, i know i had troubles with all of these things when i first got my 44 DE. as for the jacked bullets thing i mainly shoot H&K with polygonal barrels and I have never seen any type of damage from using cast lead bullets, but there are many schools of thought out there on that, thats just my .02.