Over the years, I have broken a lot of AR magazines in a lot of exotic ways. At the Appleseed shoot, I broke my very first Magpul P-Mag, and broke it in a suitably bizarro fashion.
As we were preparing to fire our first string from standing, I slapped the mag home in a brisk fashion. Perhaps too brisk. As I went to tug on it to make sure it was seated, my hand reported to my brain that maybe a little less magazine was protruding from the weapon than is usual. I finished tugging and went to hit the bolt release and it wouldn't budge. Ripping the charging handle got no results and so I rolled the carbine to port and gazed stupidly into the receiver and the problem was immediately apparent: Apparently I had slapped the magazine past the catch somehow.
After the malf had been safely cleared, I looked at the mag, and as best I can tell what happened was as follows: When I went to smack the magazine home, my trigger finger was apparently partially depressing the mag release. The nubbin of the catch that was left protruding into the well combined with my vigorous slap on the mag to shear part of the tab on the mag away, allowing the magazine to override the catch and bind the bolt.
Okay. The first step was to fling the magazine back from the firing line, rather than dropping it at my feet, where it might get mixed up with the others. The next prep period, I marked the magazine. Now the P-Mag presented me with another problem: Normally I would stomp or hammer a magazine flat before throwing it away so somebody won't get themselves killed trying to save a few bucks by fishing a busted magazine out of a range trashcan. Absent tools which I didn't have ready to hand, like maybe a hammer and chisel or a gas axe, that wasn't going to happen on this day. So I marked it very distinctively and packed it home.
I guess I'll keep it for a souvenir. Far away from my other mags.
Gun School: The place to go to break gear.