There's a bit of slop in the mag well/ magazine and how you grip the pistol and the pressure you put on the magazine can vary where the rounds strike the feed ramp. If the round hits the right edge of the feed ramp, it can stick and jam.
I had to replace a follower after trying to use a 9mm 7-round mag in my P40... the front skirt broke off. When I tried the new follower/mag in my pm9/P9... I use 8-round extended-grip mags in my K9 for home defense... every round would hit the right edge of the feed ramp and hang there. I took some pliers and tried to tweak the forward part of the feed lips to the left to direct the rounds more towards the actual ramp. The pliers slipped off both the right side and the left, and the material is very hard, so I wondered if I had done any good. With a glove on my left hand for VIGOROUS overhand racking, I had no more nose dive/hangups on the right side, so I used 400-grit sandpaper and lightly sanded the feed lips to remove any possible burrs... problem solved.
Wynn
USAF Retired '88, NRA Life Member. Wife USAF Retired '96
Avatar: Wynn re-enlists his wife Desiree, circa 1988 Loring AFB, ME. 42nd BMW, Heavy (SAC) B-52G's
Frédéric Bastiat’s essay, The Law: http://mises.org/books/thelaw.pdf
Thomas Jefferson said
“A government big enough to give you everything you want, is strong enough to take everything you have.”
and
"Peace is that brief glorious moment in history when everybody stands around reloading".