In the past week, I've noticed that when I press the mag release, the magazine will begin to drop but stop after about a half an inch of travel. To get the magazine out, I have to pull it with some force. I have found after some trial and error, that the top most round in the magazine is allowed to move slightly forward in the magazine. This is what's causing the hang up. When I slide it back into place, the magazine drops flawlessly (until the round works it's way forward again). My question is, does this generally indicate a problem with the magazine, or the rounds that I'm using?