The ACR is available in multiple barrel lengths; 8.25″, 10.5″, 14.5″, 16.5″ and 18.5″ barrels. For the 5.56mm configuration, it uses a 30-round Magpul PMag, though it is also compatible with STANAG magazines. Magpul claims that PMags are much more difficult to break or damage than other magazines, and is also compatible to other rifle families like the M16 rifle family. The ACR was engineered to still function reliably even if it was exposed to sand, dirt, mud and water.