that will work in the Thermold m1a 20 rd mags . I keep mine loaded when in storage and there are always loose rounds in the box after a few days. I look at the feed lips and they are a different shape than the Pmags which work. The bullet end tilts up over time and a slight hit will pop one or two rounds. Since I cannot add to the feed lips methinks a real anti tilt follower w/longer legs could solve the problem. Asked thermold and there suggestion was to just load 17 or 18 rounds for storage. Already tried that with down to 15 rds and it does not do any good. How do make a slight hit? Just not well coordinated sometimes when loading. Good news is the mags lock up tight even w/20 rds and the bolt closed and the one I tried shooting with ran. Any thoughts on a source? seabreeze BTW, my mags have the old 8 coil springs and I understand there is an upgrade to 9 coil new springs and maybe a better follower. Anyone heard about that?