I have a build (my first) that i think has a slight problem somewhere. It shoots and runs all my mags fine. But it wont lock open on an empty mag. I can manually lock it, and if i pull the bolt open slowly on an empty mag it will catch. But normal shooting or quick cycling and it wont catch. Is there something i can adjust? ITs almost like the mag spring is not quite enough to get the bolt catch high enough. But they are all pretty new Pmags. Suggestions?