The Black Dog Sonic X magazines are constructed from glass filled nylon with nylon feed lips. The magazine is easily disassembled for cleaning and maintenance. The translucent polycarbonate allows you to see how much ammunition is remaining in the magazine. They are compatible with Atchison, Ciener, CMMG, Spikes Tactical, Tactical Solutions, and Target Master Conversion kits and uppers. These magazines also work with Sig 522, and Kel-Tec PLR22 firearms.