Jboy,
One other I remembered, and is a simple thing that you might try. Load the magazine with the cartridges located in different positions. i.e. try loading with rounds slid all the way back in the mag, all the way forward, and midway when they are in the mag. When I was at the range, I remember getting an occasional feeding problem with the bolt not wanting to pick up the cartridge as well and it turned out to be when the cartridges were too far forward (they are in the mag but the tips are almost touching the front face of the mag). When I moved the cartridges back, the feeding problem was solved. Experiment with different arrangements and I suspect you might have the same experience I did.