Mk18 Mod 3 CQB Upper Receiver Group - Colt Geissele 11.5" URGi

Assembled to Order, expect 3 to 5 week lead time for Surefire muzzle devices

Mk18 Mod 3 11.5" Colt Geissele URGi Upper Receiver Group

the 2019 US Military updated Mk18" Upper Recevier Group with 11.5" barrel - the new standard in close quarter battle rifle uppers CQB




Custom built Mk18 Mod 3 URGi features the new 11.5" Colt barrel with 10.5" Geissele Mk16 rail and a Colt upper receiver, with just the right trimmings.  Built to the newest military standards, and professional assembled by Potomac Armory for Charlie's.  The 10.3" Mk18 is a classic, but time has shown that an 11.5" barrel performs better with a wider variety of ammunition without adjustments to the gas port or the buffer weights.  The "upper receiver group improved" 11.5" Mk18 performs best with a heavy (H or H1) carbine buffer.

Geissele has proven the Mk16 upper rail to USASOC in the URGi for M4A1 in 14.5" barrel, and now the Mk16 is showcased in the new Mk18 Mod 3.  The barrels are either Colt or Daniel Defense government profile chrome-lined barrel, both of which have been used widely by miliary and law enforcement units.  As an added bonus, the Surefire SOCOM 4-prong flash hider comes as an option, perfectly timed and rockset into position.  This upper receiver group will accept any of the Surefire SOCOM series of suppressors.  Charlie's prefers the SOCOM mini, as the length is appropriately sized to the short barreled upper.  To prevent gas blow-back, especially in suppressed mode, the Mk18 Mod 3 comes standard with the PRI M84 military Gas Buster charging handle.  Charlie's has chosen the Geissele blackened gas block, which is expertly set in-place with lower screwed set screws.  The end-user has the option of additional through the barrel pinning (which is recommended for extreme duty, but not necessary for most law enforcement and recreational shooting needs).  You also have the option of choosing a Troy gas block.  The Colt upper receiver comes standard with a Colt bolt carrier group.

Note:  the forged upper receiver will fit any mil-spec lower receiver.  Colt is recommended, but other military grade forged lower receivers will fit as well, e.g., LMT, KAC, FN.  Commercial forged and billet receivers will fit, but are not recommended with this military grade upper receiver group.

NFA notice:  This upper when assembled to a rifle lower and stock becomes a short barreled rifle (SBR) which is subject to registration under the National Firearms Act.  If assembled to a lawful AR pistol lower without a stock, this item can be used as part of an AR pistol.  Be sure you understand the laws concerning SBRs and AR Pistols.

pics courtesy of Potomac Armory, Geissele and u/GS556 from Reddit


Upper Receiver                                                                               

Colt M4 military grade forged upper receiver, 7075 aluminum hard coat anodized with M4 feedramps and engraved and painted top T marks.  CAGE Code marked


Either Colt or Daniel Defense 11.5" military grade barrel:  1:7 twist, Steel allow CMV barrel, phosphated exterior and chrome-lined.  HP/MPI.  5.56 NATO chambered and 1/2" threaded with 28 thread pitch


Bolt Carrier Group

Colt military grade High Pressure tested and Magetic Partical Inspected carrier and bolt.  Military grade staked gas port.  Test fireed for tested.  Bolt is marked MPC. 


Upper Ral / Hand Guard       

Geissele Mk18 10.5" military grade upper receiver, roll marked "Geiselle Automatics"  Hard coat anodized in DDC with T-marks engraved and not painted, as per military spec in the URGi.


Muzzle Device

Standard with no flash hider, options for Surefire SOCOM 4-prong flash hider FH556RC, Surefire SOCOM 3-prong or Surefire Warcomp 3-prong expertly timed and secured with Rocksett.  Note:  we time the Warcomp in Neutral positon.  If you prefer the partially offset gas port, just let us know i the comments.


 Gas Block

low profile Geissele Super Gas Block, black oxide blackened, and set in place with lower set screws.  End user has the option of adding a drilled through the barrel pin, if extreme use is anticipated.  We also offer Troy gas blocks as an option, just let us know in the comments


 Charging Handle

PRI gas buster charging handle, M84 with military latch


 Country of Origin

Made in USA with all component parts military grade made in USA



5.56mm / .223 caliber


 Recommended Ammo

Accepts all common ammunition.  55, 62 or 77 grain recommended