Most of today's AR .308 magazines are limited to just 10 or 20 rounds, which can be a pain for the range junkie who's looking to spend more time shooting and less time reloading. These polymer AR .308 magazines provided an expanded capacity, with 30- and 40-round magazine available to fit standard DPMS and SR-25 rifles.Each AR .308 polymer magazine is built for use with the .308 Win. cartridge, and the magazine body is constructed using DuPont's proprietary Zytel polymer, which has been proven to be durable and long-lasting. Constant spring pressure is provided by a heat-treated chrome-silicon wire spring. The magazine are all made in the USA and feature an all-black finish.