I have found that the angle of round as it leaves the magazine is crucial. Also the spring had to be tuned to the ammo. Most of my problems were cured with a pair of needle nosed pliers and a little bending in of the top of the mag at its narrowest. About center above the magazine follower. I just measured my functioning FXO mags and they came out to about 4MM wide where the angle is formed.
I'm not a gunsmith, but I have done this with 50 or 60 mags and it has worked. Be careful! <img src="graemlins/yltype.gif" border="0" alt="[typing]" />