The SIG Sauer 522 LR is a .22 LR semi-automatic, blowback operated rifle. It is patterned after the SIG 55x series rifles that fire 5.56x45mm centerfire cartridges. The 522 fires .22 LR ammunition and serves as a training rifle for its larger counterparts due to mostly identical controls and features. It differs from its centerfire counterpart in a number of ways. The 522 series has no adjustable gas block as the 55x series does. Instead, a mock gas block is installed. SIG refers to this as a storage container. Instead of 30-round magazines, the 522 series accepts 10-round or 25-round magazines that are manufactured by Black Dog Machine and re-branded for distribution with the SIG 522. Black Dog also produces a 50 round drum magazine for the 522.