Cowboy Blob had some 9mm AR questions and, slacker that I am, it took me a couple of days to remember to drag out the gun and the camera at the same time.
(Apologies for the photo: I had to hold the camera with one hand, the mag with my other hand, and use one foot to keep a cat from scaling Mount AR.)
(Yeah, it's about 250 rounds since the gun was last cleaned. It's a torture test, or something...)
The gun is trouble-free so far, but all I've run it with were Colt 32-rounders. I have an RRA-modified Uzi mag as well, but have yet to try it. The main visible difference between the mag catch holes on both is that the Colt mags have square holes (like mags 1 and 3 in CB's picture), while the modified Uzi mag has a rounded leading edge (like mags 2, 4 and 5).
One noticeable difference: My mag block doesn't stick up anywhere near as far out of the lower...