As you can see the notch on the top of the spine is slightly narrower on some of the XCR-M pistol magazines. It is the one on the right. Some fit fine, some don't. You'll need to open the notch up a bit with a file...on the left side looking at it, for the bolt to release on an open bolt. There seems to be some slight variation on the mags.
I'll post another mag shortly.

I'll post another mag shortly.
