We had a situation in class a few weeks ago where a student dropped a PMAG on the hood of a car during a bail-out drill. As the teams bounded back, another student engaging a target forward of the same car put a .30 caliber AK round through the PMAG.
As you can see in the photo, the mag spring was cut in half and the mag cracked up to the mag catch detent. As we were walking back after the drill, we noticed the follower still moved under spring tension. So we loaded a few rounds into it and tested it, with the cut piece of spring sticking out of the side. See the video link for the results.
After that demo, I pulled the spring out, tossed the cut section and stretched out the remaining 3/4 of spring. We reassembled the mag and loaded it with 28 rounds. The second test fire is in the video too.PMAG Test
I don't see metal mags passing this test. The magazine shown above continues to be run in classes...