I know magazines are supposed to be suspect #1 with most semi-auto firearms, but that does not hold true in my experience with the Ruger Mk II. I'd make sure your gun is clean and LIGHTLY lubricated with a high quality product designed for firearms. Pay particular attention to the large slot in the bolt and the bolt stop pin. Next, I'd order and install a Volquartsen extractor. While you are at it, put in a trigger shield. Both available from OnTarget. Trigger shield will save lots of cleaning time. My Ruger took almost 2,000 rounds to break in, but has been great ever since. Good Luck.