The AR-20 was introduced and was the initial designation of Armalite’s .50-caliber rifle. The designation was later changed to the AR-50 to emphasize the caliber of the firearm. This period also brought the introduction of a few devices to help test and train the Mk 19: the AR-22—a Blank Firing Device for the Mk 19 Mod 4 40mm Grenade Machine and the AR-23—a Sub-Caliber Training Device for the Mk 19 Mod 4 Grenade machine gun. The AR-30 was also introduced during this time and is based on an aluminum stock that merges a machine rest with a rifle stock for stunning stability. This design is immune to changes in temperature or humidity.