I built an all new AR pistol chambered in 300 AAC BLK. I used all new parts. The barrel is from AAC and is 9 inches with a pistol gas system. I used the H2 buffer that AAC says I should use. I took it out today and fired 30 rounds only. I had 1 double feed, and twice the bolt did not go fully into battery. It like got stuck, it would not go forward or come back out. Anybody have any idea what might be going on? Is it just because it is all new and needs some break in time, or is there a problem? I was using new 150 grain supersonic rounds.