FBI HRT Geissele Mk4 Federal Rail and Barrel Kit - 11.5" Colt

ships from our shop in 3 to 5 days (+/-)

FBI HRT Federal Rail and Barrel Kit - 11.5" Geissele - Colt

Starter build kit with Geissele Mk4 Federal FBI rail

Charlies Custom Clones brings you the HRT Federal Green rail and barrel kit.  This is a great start for an FBI HRT clone rifle build.  Charlie's has partnered with Potomac Armory to bring you a balance of the right parts and not break the bank.  This is the current production Geissele 10" OD Green Federal (FBI) rail with laser etched T-marks.  We feature a Colt factory 11.5" Chrome-line Government profile barrel, in 4150 chrome-moly-vanadium steel (CMV) with a factory installed Colt low profile gas block, drilled into place.  The Colt low profile gas block is a remnant from the A-frame front sight base, but Colt has shaved down into an integrated gas block.  Colt offers this barrel on hits performance series EPR rifles.  The gas tube is factory Colt as well.  So, you get the best in performance wtih a factory Colt barrel, complete with factory Colt markings.  A Surefire 4-Prong 'fast attach' flash hider rounds out this offering.

The rail and barrel kit will fit a mil-spec upper receiver.  Potomac recommends forged receivers, like Colt, LMT, Daniel Defense, Bravo Company, FN or Rock River to name a few.  Billet receivers sometimes do not do as well timing to the Geissele rail.

Note:  All items arrive in a box, unassembled.


  • Geissele Mk4 Federal 10" OD Green rail with laser etched T-markings
  • Colt 11.5" factory barrel with an M4/Government profile CMV 4150 steel with mil spec phosphate black/gray finish, 1:7 twist 556 NATO chambered barrel with chrome lining
  • Surefire FH556-215A Fast Attach 4-prong flash hider (this is an earlier model and will fit FA556 suppressor, but not the SOCOM generation suppressors) with DLC black coating
  • Colt factory installed low profile gas block with two taper-pins through the barrel to keep the barrel in place, while being able to remove, when needed.
  • Colt premium military contract carbine length stainless steel gas tube
  • Geissele barrel nut and bolts to attach
  • smaller Allen wrench for tightening Mk4 rail tabs
  • gas block roll pin for attaching the gas tube
  • Surefire indexed washers for attaching and timing the flash hider
  • Small Rockset tube to apply to barrel to attach the flash hider

Note:  for the same kit with a Daniel Defense barrel, see here:  HRT FBI barrel and OD Green Geissele Federal Rail Kit with DD barrel