I know Magpul recommends the dustcover accessory to take the strain off the feed lips if you store your Pmags loaded. Lancer L5AWMs have the steel feed lips so no storage issues there, but what about all the other poly mags like Thermold, Hera H3, Troy Battlemag, TangoDown ARC, Tapco Intrafuse, Hexmag, etc? Is loaded storage a big no no with poly mags other than the Pmags and L5AWMs?

Has anyone had any warping or issues with loaded poly mags in storage from brands other than Magpul and Lancer?

Magpul no longer says that the dust covers are needed for long term storage. Apparently you can keep them loaded indefinitely and not worry about damage to the feed lips. I'm not sure about other polymer mags...with the price of PMags being as low as they are I see no need to buy anything else!

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Part of the big key to the Magpul design is that one can really put 31 rounds in a 30 round mag. This keeps the spring from being completely compressed and the feedlips are not under maximum stress. Additionally today's modern materials are some times better then steel. Just this week I had an aluminum mag start causing jamming after about every 3rd shot. I am buying all new black Gen M3 Pmags and leaving them loaded at 29 to 30 rounds with the dust covers on. Mag comes with free dust covers, might as well use them.

I was always a metal mag fan, but not anymore.

I have  around 6 gen 1 PMags that have been loaded for 4 years or longer no issues. I did pick up 2 20 round lancers last month and am deeply impressed the design seems very well thought out and it must take some real time to seemlessley  blend the metal and plastic like they do.

Is that what those magpul top clips are for? Holding the lips tight?
lol
Was wondering why they made such a fancy dust cover.
They don't work on the 15/20 mags because the tollerance is too close.

Yeah, the dust covers actually push the round stack down off the feed lips about 1/8 of an inch so there's no strain on the lips during storage.