This a Bushmaster Upper in 5.56mm with 20" Chrome-Lined chamber and bore. It's a 1/9 twist with a GOV'T profile so its NOT and HBAR (heavy barrel). Flat top with Tmarks. Has optics ready F marked gas block with bayonet lug and A2 Flash Hider. Comes with Bolt Carrier Group and Charging handle. SOLD SOLD SOLD!!