Beyond round count. Another deal are drop tests. The Gen3 PMag gets little cracks, so it fails, although still functional. The aluminum one bends all to chit, binds up and fails to function, although it doesn't crack and passes the test. Sounds very sciency. LOL
This, copied and pasted may be of interest... From a pretty good discussion.
https://www.m4carbine.net/showthread.php?193786-Why-PMAGs-are-better-than-aluminum-USGI "To add a few points...yes, you can drop an M3 and break it after a few drops if it hits right. Your USGI Mag would be non functional at the same point, however, and the cracked PMAG will still feed fine.
Yeah, there were some tweaks required to the 2007 PMAG for some guns. A decade ago. The M3 stop is there for a good reason, and if you want the other benefits of the mag, yes lowers that deviate from normal dimensions require alteration to the stop...but if you don't have a weird lower, it's a complete non-issue. Certainly not for anything built to TDP.
M3's were not redesigned. A tiny rib was added to deal with ammunition on the smaller end of SAAMI spec that could exhibit the transposition issue. Never was an issue with function, and apart from a few outliers, only on the early M3 20 did it prevent insertion when combined with the right rifle and ammunition. We made the change anyway. We have test data both before and after the change, and it doesn't affect anything else. Sinlesssorrow, why didn't you swap those out? You still can. If you're seeing the issue with mags you have, just swap them for new ones. We'll gladly do so, as has always been our policy.
We've long ago covered the whole long term storage thing on this very forum. There are plenty of guys in service right now who have PMAGS that have been on 3, 4, or more deployments. So that part should not be in question.
Lots of folks want to give USGI mags a pass, "Oh it was old" or "it was past service life" or "you just didn't take care of them". I'll agree that the USGI is not a "bad" mag with many ammunition types in certain iterations, although every change picatinny has made has seemingly made it worse. What cannot be said, however, in the face of the body of test data that now exists, is that the USGI is "as good as" the PMAG M3 and certainly not better by any stretch or interpretation of data. Not clean, not dirty, not with multiple types of currently issued ammo. Maybe extreme long term longevity in protected environments without rough handling, like non-maneuvering range use.
It's fine if someone "prefers" USGI, or any other mag, for form factor, fit in pouches, familiarity, or whatever. There's just not much of an argument that can be made based on feeding performance to support any choice other than PMAG GEN M3, especially with currently issued ammunition types.
Duane Liptak, Jr.
Executive Vice President
Magpul... "