NOTE: This is a blow back design. A gas tube and gas block are not needed.The barrel is one of the most critical components of your build. We only offer high quality barrels so you can be confident that your rifle will be off to a good start with which ever barrel you decide on.Features: 5.5" Length Barrel 1/10 Twist Rate 1/2 X 28 Thread Pitch for Muzzle 9mm Luger Chamber Black Nitride In and Out Weight: 10oz