The round requires a special M2 Training Bolt that changes the weapon from locked breach gas to straight blowback operation. Once the bolt is installed-—which takes about 30 seconds—-the weapon will work normally in semi- and full automatic operation. It works in standard 20-inch barrels and also in M4 carbines with short barrels. With the standard bolt installed an SRTA round will chamber and fire but the gun won’t cycle or extract.