[Sionnach]

The following is from a Danish soldier's web site, http://www.tactical.dk/uk/tactics7.html. The magazines he mentions are not Magpul, but they are polymer.

Another magrelated malfunction. Check the distance between the feed lips. No I don't know the correct space measurements, but I have noticed a significant larger space on some Thermolds than on alu and steel mags. This is a sure sign that the Thermold is going bad. If anyone knows the correct space between the feed lips, please let me know.

This is a common problem when using our issued crappy Zytel Thermold mags, but again it's mag related. Not really the fault of the rifle. What happens, with the Thermold mags, are that they crack at the bottom of the right feed lip, and then the rounds can freely exit the mag. Quite simply, the mags don't have a long lifespan when they are kept loaded for an extended period of time. Plus when unloading the rounds from the Thermolds, don't take them out at the top of the mags, but rather remove the bottom plate. Reason: Because it strips off small pieces of the plastic from the feed lips every time a round goes out from it. That means even when you are just out shooting, the mags are being worn out by this. And using the mags while shooting full auto eats up the mags even faster, giving them the nickname of "Thermelts". A second reason to throw the Thermolds into a campfire.

I have experienced this on numerous occasions and have started purchasing the U.S. Issued Aluminum mags, instead. Also the steel FNC/Swedish AK-5 mags with a new green follower from a U.S. alu mag is good. Since using them I have never experienced it. It's pretty embarrassing having a fountain of 5.56 mm ammo ejecting from your mag on the range, in battle it could cost lives.

Since the army is probably set on keeping the "Thermelts" Go purchase your own Alu mags, your life greatly depends on your mags ability to hold rounds until needed. (Incidentally, the Canadian Army dropped the Thermolds, for the Alu type. Hmm.....Ring a bell, anyone?)