All right, I think I've got it figured out. I found that if I release the bolt and slow its forward travel even in the slightest bit it'll jam. Anything less than an absolutely perfect release won't work. Sometimes it still jams though, usually on the last round. I'm guessing this is an issue with the follower plate? The jamming seems to lessen with repeated use, so maybe the rifle is just getting broken in.
My mags all had the circle-OTK mark and most had the crossed swords. It was hard to tell under the paint. They were all used but the feed lips looked pretty good.
Another thing I noticed is that after being cycled through the gun, the cartridges had very light dents in the primers from the firing pin. Is this normal? I don't know exactly how deep the dent has to be for detonation, but I sure don't want to find out when I'm not at the range.