I've had some time to experiment with it since I last posted on this thread about it. The gas block is a picatinny 4-rail type and it butts up against the free float handguard when everything is installed. It looked like the gas block might not be sliding all the way back, so I decided to try it without the handguard to see what might happen. As it turned out, that made the difference. There's probably about 1/16-1/8" that needs to be taken off the front of the handguard. The load I was previously trying now ejects the brass and picks up the next round, although it doesn't hold the bolt back on an empty mag, so it probably just needs a bit more powder. It's not that big of a deal for me since I don't routinely carry multiple mags with me anyway.
I was developing a load for my nephew and his .300 AAC last weekend and had a round come out the side of the barrel that is used for a bullet stop with deceleration media. We looked at the wall behind it and could not see where it had hit. I was cleaning the garage on Thursday and came across one of the jacketed bullets that he was using. It had rifling marks on it, so it must have been the one that ended up going through the side of the barrel. I'm thinking that the bullet hit someone along the way (possibly another bullet) which upset it's flight path enough to make it go out the side of the barrel while tumbling and then hit the back wall sideways, but so slowly that it did not put a dent in the wall. It then made it 12 ft or so before coming to a stop. There's a 1/2" steel plate in the bottom of the barrel and there were no marks on the bullet that would indicate that it hit the plate before coming back out.