Custom upper build from Potomac Armory, made originally for federal law enforcement agencies. This is an HRT style short barreled upper receiver is now available for civilians, as a limited edition.
Made with traditional FBI spec'd parts, the FBI upper is similar to that used by HRT and regional FBI SWAT teams. Starting with a premium law-enforcement spec premium forged 7075 M4 upper receiver and premium mil-spec bolt carrier group, the FBI upper receiver group sports a Geissele 10" Mk4 Federal rail in OD Green, with pronounced Picatinny rails at the forward end for tactical attachments. Troy folding M4 back-up iron sights are standard, and the operator can choose a Colt FBI 11.5" heavy profile barrel, or a Colt 11.5" government profile barrel, both with Troy low profile gas block, and a choice of tactical flash hiders from Surefire, BE Meyers and Knights Armament, to support a variety of suppressors.
The Colt FBI barrel is coveted by many collectors, and has Colt markings under the rail. The Colt 11.5" Government profile barrel comes with your choice of a factory mounted two-pin low profile front sight gas block, or with the front sight block removed and a Troy gas block installed. If you choose the Troy block, the front pin groove where the front sight was pinned will be chemically blackened, and visible if you look real hard.
The FBI URG from Potomac Armory is quite capable, and very versatile. The 11.5" Colt FBI barrel performs very well with fully automatic fire, while the Colt Government profile barrel is quite capable of suppressed or unsuppressed fire.
The Aimpoint T-2 optic is optional, and mounting options offered are a Daniel Defense riser mount (SWAT model) or the Spuhr HRT version.
NFA Notice: This upper receiver group, when mounted on a rifle lower receiver becomes a Short Barreled Rifle (SBR), which is tightly controlled and registered by the ATF. You may mount this upper into a lawful AR pistol lower, and not have an SBR. Be sure to understand the NFA laws and your local and state laws to make sure you can lawfully own this. Also note that mere possession of a short barreled upper and an AR rifle lower in close proximity may be a violation of the NFA.