I was at the range this weekend. In order to be able to find my brass after shooting my HK33 pistol clone, I draped a hand towel between the ejection port area and my range box. It worked fine for the entire session(50 rounds) with one exception. About 40 rounds in, the towel I used slipped down, and a brass casing was kicked back into the action. The bolt was only half closed and I could see the brass had nose-dived towards the magazine feed lips. When I turned the rifle to the side to clear the action, the round would not fall out. I removed the magazine and, to my surprise, the empty round had imbedded itself into the plastic feed lips of the magazine. I pried the brass away from the mag, which took quite a bit of effort, and it left this horseshoe-shaped cutout(sorry for the poor optical quality, but it's as clear a picture as I could get):
The spent round in the mag is to hold the follower down so you can see the cut. I continued to use the magazine, and the piece did not break; however, my MKE mags are definitely for range use only now. A shame, too, since I have had no other issues with these mags in hundreds of rounds.

The spent round in the mag is to hold the follower down so you can see the cut. I continued to use the magazine, and the piece did not break; however, my MKE mags are definitely for range use only now. A shame, too, since I have had no other issues with these mags in hundreds of rounds.