This 16 inch barrel for the AUG converts the AUG from 5.56x45mm to .300 AAC Blackout. With just a push of a button, the 5.56x45mm barrel can be removed and replaced with the .300 AAC Blackout barrel. This conversion requires no tools or any additional parts. The .300 AAC Blackout barrel is capable of firing both super-sonic and sub-sonic ammunition. The adjustable gas regulator has six settings. The barrel is threaded 5/8 x 24 and sports a 1:8″ twist rate.