I noticed the problem even before getting the mags fully loaded, they weren't even in the rifle yet. Besides, I've done the "drop free" bolt modification. Even if the feed lips are damaged, the magazine spring should still push the cartridges to the top, not stick part way up. They feed rounds fine when only half full.
Update: I took the mags apart and sprayed them with some dry lube I had in the garage. They now seem to function better. When full, they now pop the cartridges up when I push them down and release. I'll try shooting them again in a couple of days. Thanks for the replies.