OH NO!!!!! My mini is doing it too!!!!!! It started when I switched from Winchester brass to Lake City. Me thinks me fixed it! I thought it was, because the military brass was tough, and eventhough I full sized it, it would misfire. I noticed when it misfired there was just a hint of a fireing pin hit, BECAUSE the bolt dosen't go all the way home, BECAUSE the "Extractor" does not always open enough to grasp the brass, BECAUSE: (1) The chamfer on the case head is very small on the Lake City brass, compared to the Winchester brass. (I'm talking about the very first surface which strikes the extractor, not where the extractor grasps. The smaller the chamfer the larger the surface trying to force open the extractor. Check out your brands of brass) (2) I removed the bolt, and held an empty case on the bolt face, and pushed it in and out a few times (pushing straight in it was dificult), I noticed the radius of the case head did not exactly match the extractor radius, there seemed to be a raised portion on one end of the extractor which formed a burr. The angle of the burr resting on the case head, I could see why it was difficult to open the extractor. Using a jewlers file, fine stone, and smoothing with 600 grit sand paper, I reduced the burr only, and matched the chamfer of the rest of the extractor radius. Cycling it manually it seems to work now, will know for shure when I get to the range. I hope this gives you guys a couple of leads to solve your problems.