I have had some failures to feed and it appears to be related to increased friction when the bolt is trying to close. I attributed this behavior to the rifle being new and the parts needing to go through the typical wear in process. But it appears that it might be related to the C Products magazines. I was reading on AR15.com that many of the users are experiencing all sorts of problems with the 7.62x39 30 round magazines. There was mention of a bad batch of magazines that were sent out by C products.