The Dirty Bird Industries M16A1 20" 5.56 Retro Upper Assembly is the next iteration in the line of DBI's popular Complete Uppers. Dirty Bird Industries has sourced some of the finest parts in the industry to make sure that this complete upper is not only a great throwback build and aesthetically accurate, but also performs flawlessly in the field by taking advantage of modern enhancements to the platform.Notable enhancements include: 1:9 twist instead of 1:12 which will stabilize a greater variety of bullet weights and a black class 3 type 2 anodizing to match most modern mil-spec lower receivers.20 5.56 Lightweight Contour 1:9 Rifle Length Barrel w/ FSB Chambered in 5.56 1:9 Twist Rate Button Rifled A2 Front Sight Base w/ Front Sight Post InstalledM16A1 Assembled Upper Receiver 7075-T6 Forged Aluminum Factory Installed Teardop Forward Assist & Dust Cover Factory Installed Dual Aperture Rear Sight Fully Compatible with any Mil-Spec Lower ReceiverA1 Triangle HandguardA1 3 Prong CompensatorMade in the USA - Backed by Dirty Bird Industries' Limited Lifetime Warranty