So I have a Beretta CX4 rifle in 40s&w, this one takes 96 mags.   Shoots fine with the 2 factory 11 round magazines. But when I try the mec-gars it becomes a jam-o-matic. The rounds are nose diving instead of chambering correctly. I have 2 of the 13 rounders and 2 more with the +2 base pads. All four are having this problem. Even tried different ammo, so it is the mags. I hate to start bending on a  pricey mag. Took them apart and the followers and springs are fairly different between the factory and mec-gars. Maybe try factory followers?

Anyone else had any issues with these?

Article in Tactical Weapons March / April 2009 about this rifle being used by College of William and Marry Campus PD. They really seem to like this weapon and have it teamed with the Px4 pistol. Both are in .40 S&W.  They did not mention any problems but they did go to the larger 17 round mag which allows for fast / easier mag removal. If it was mine and the after market mags gave me problems, I would bite the bullet and go with factory mags.

Try popping a follower out of your working mag into one that doesn't work and see what happens.

Well of course I tried that.

The way the mec-gar mags are made will not let the factory followers reach the top of the mag.  Something is wrong with these mags, I really think they are for a 9mm. Odd because I bought 2 from 44mag and 3 from brownells.

I don't know about Mec-Gar Beretta mags, but I can tell you that the feed lips of a Beretta 96 mag are slightly wider (no surprise) at the top than a Beretta 92 mag.  If you were to put them side to side, and look at them from the back, the cut that looks like \__/ will be wider for the .40.  Sounds like you've already looked it all over. Sorry if I'm suggesting the obvious.