Thermolds were not and are not designed for loaded storage. If you keep them downloaded by a round or two and if you don't store them loaded they will usually work just fine. Interestingly, when I first started using an AR, that was the same advice given for the GI aluminum mags (20 round) that we were given...download and don't keep them loaded for a long period of time. Having said that, I've got 30 round Thermolds that I have been using and abusing since the early 1990s that have been just as reliable as my GI 30 round mags.