So a buddy was having feeding problems, mostly with cross-mags. Turns out, on an open bolt, you can over-insert them by like 1/4". The mag slips right past the mag catch, and it latches when you pull back down on it. Wasn't as bad with pmags, or steel LAR mags. All of his cross mags have bullet point indentations in them from the bolt plowing rounds into the front of the mag instead of lifting them up into the chamber. Also seems like the follower in the cross mags might be a little lazy, which makes the problem worse.
...Now that I think about it, I didn't check if his mag catch was adjusted properly. Probably should have done that. Ah well.
Tough to pick up on that via text. Sarcasm makes much more sense there, lol