Would anyone know what would cause an AR bolt to not close all the way when trying to chamber a round? Both my Brother and I experienced this on FIVE AR rifles today at the range. We were using both factory, and reloaded ammunition that I painstakingly loaded myself. This was in BOTH .308, and .223 versions. In the case of my personal AR rifle, I had just given it a thorough cleaning. Usually this helps the rifle operate BETTER. Not in this case apparently. I have had over 800 rounds through it BEFORE I ever cleaned it, and NEVER had a problem with it. It ran perfectly when it was filthy. Also, when the bolt(s) incompletely chamber the round, it 'locks' closed, necessitating the use of a rubber mallet, and a block of wood to open the action. The rifles were all a perfectly clean as possible, bolts, chambers, gas tubes, etc etc. My Brother has had this probelm before, but not as pronounced, and I have NEVER had it before. Would anyone know what the problem may be, and what the remedy is? Different magazines were tried as well. Today was not a good day at the range. Thanks all.