OK, I now know what the problem is. I have what they call "patented bullnose followers" on the CM mags. Per the Checkmate website, the patented bullnose follower takes a different spring because standard springs won' fit between the bullnose and the tab at the rear, and the bullnose pushes down on the spring instead of slipping over it.
Checkmate is out of stock on springs for the patented follower, so I can't get their springs. ISMI has what they call a "Narrow Follower Magazine Spring" so I ordered a few of those to see if they will work with the CM patented follower.
