Took the mini to the range this afternoon to try out the new 30 round magazines that I purchased from Cabelas... which didn't fit properly. Anyways, the real problem is that when I fire a round the bolt never retracts and the shell stays in the barrel. I recently took it completely apart to put a tactical stock on and while it was in pieces I cleaned it thoroughly. after reassembly I oiled it and put it away until today. I am shooting factory rounds and have not shot steel through it at all. any thoughts on what could be the culprit?