I have had the same issue with Wilson ETM, Wilson 47, and Tripp Research mags. I called Tripp and they said to send their mags back to them for tuning. They also explained that slamming mags in with a slide-lock reload causes the inertia of the ammo in the loaded magazine to expand the lips at the top of the mag. This is even more prevalent in the .45 mags. Anyway, they tuned my mags and all went back to dropping free. All it cost me was the shipping to and from their shop. However, that was some time back and some of the same issues have arisen. I just haven't sent them back in for tuning yet. I wish I had the dies or whatever is necessary to do this mag tuning myself.