I took a new Colt 20 inch barrel and had Kurts Kustom Firearms cut it to 11.5 inches, recontour the barrel, thread it, crown it, put a new gas port in it, and repark it. I then mated it to an A2 upper receiver and put a Pigtail gas tube on it. I checked the ROF with a PACT timer. I had the upper mounted on a Colt M16 lower receiver with a collapsible stock. With South African ammo and a standard buffer, the ROF was 782 RPM. With an "H" buffer, the ROF was 757 RPM. With a Colt "C" buffer, the ROF was 615 RPM. If you want the complete upper, it comes with a new M16 bolt carrier and a new Colt bolt. The whole unit is $525 + S&I. If you do not want the bolt carrier and bolt, then the unit without these parts is $400 + S&I. I guarantee all the uppers I put together. If you are not 100% satisfied, return it to me for a refund. All NFA rules apply. This upper must be used with a registered lower receiver.
Alamo Professional Arms