Many years ago, I had a very similar problem with my then, brand new S&W Pro Series 9mm 1911. It was after experiencing the same problem that I started looking at the mag release and figured out what was going on. Like you, I found that they wouldn't drop free at the most inopportune times...PPC match or other competition shooting. Never a problem on the range or during practice. Under the "stress" of competition, I has hitting the mag release with a much more pressure..."pinning", or locking the mag in the grip frame. (EDIT: The gun came with Wilson Elite Tactical mags) The inside curvature of the mag release button was a tad too "thick". Any less pressure, a normal depressing of the button, and the mags dropped free. I called S&W and the very kindly sent me two complete mag release assemblies. That way, they said, I could "machine one" and have another if I took too much off. A couple dozen light passes with a half round file was all it took. Now, even a gorilla grip on the mag release doesn't keep the mag from falling free. It is still fully secure in the frame whenever the mag release is in it's normal position and it has never fallen out on its own since the fix...10 years ago.