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

$1,199.00 - $1,699.00
Assembled to Order, expect 2 to 4 weeks, depending upon part availability

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

the 2019 US Military updated Mk18 Upper Receiver Group with 11.5" barrel - the new standard in close quarter battle rifles.  The Army calls this the CQBR - URGI


Custom built Mk18 Mod 3 URGi features the new 11.5" Colt chrome-lined phosphated military spec 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 military and law enforcement units.  As an added bonus, the Surefire SOCOM 4-prong flash hider comes as an option, perfectly timed and Rocksett into position.  This upper receiver group will accept any of the Surefire SOCOM series of suppressors (except for the Fast Attach 215-A four prong option). 

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 a low profile long nose gas steel gas block from Sadlak, which makes many of the gas blocks on the market today, under various brand names.  The gas block is set with two set screws into dimpled barrel and red Loctite in place for a secure setting.  We also offer a Geissele blackened gas block, which is expertly set in-place with lower screwed set screws, as an option, for an additional cost.  If interested, contact our sales team.  We do not think it is needed, but many like the Geissele gas block, and it will come with barrel pinning (which is recommended for extreme duty, but not necessary for most law enforcement and recreational shooting needs). 

The Colt upper receiver comes standard with a Colt bolt carrier group.  Colt is currently using Brass Aluminum Company forgings, with the "square" forge marking and CAGE code markings. 

Charlie's is currently sourcing both Colt and Daniel Defense barrels, and barrel supply is very hard to get, so this is not a choice, but a matter of which company is supplying us with barrels at any given time.  Later, we might also offer FN barrels.

Mostly, we have Colt barrels, as DD has stopped shipping barrels in early 2021, and we do not expect DD barrels again until early 2022.  The barrels both meet military standards, and both are carbine length gas system Government profile, chrome moly steel alloy phosphated exterior with 1:7 twist and 5.56 NATO chambered and chromed lined.  The Colt barrel is generally preferred, but Daniel Defense makes a barrel just as good.  The Colt barrels come to us either new, or are take-offs from LE6933 or the LE6933 EPR short barreled rifles, and may have had the front sight base removed, or come with a Colt installed low profile gas block (from the EPR rifle).  

Note that with the barrels, we have several options for gas blocks.  The military clone correct option is the Mk12 gas block, and this is done in a Crane-style since the barrel will have the forward taper pin groove from the removal of the front sight post.  Exactly like the US Navy SEALS used in the original Mk18 Mod0.  The forward taper pin groove is chemically treated to both blacken and protect from the elements.  A Colt factory installed low-profile gas block is also an option, as is a Sadlak long-nose low profile gas block, which will cover any pin groove.  Finally, a Geissele "bomb proof" installed gas block is also an option, for the price of the gas block and a very most shop charge to drill and pin the gas block in place.

With this Mk18 Mod3 / CQBR URGI, you have your choice of several Surefire muzzle devices.

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.  


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

Colt barrels are new, but could be take-offs from other new rifles, and may have grooves from where a front sight base was installed.  Any grooves will have been blackened and covered by the long nose low profile gas block. 

Colt barrels generally are CAGE code marked near the muzzle.  Daniel Defense barrels will be stamped between the breach and gas bock, and might not be visible without removing the rail.


Bolt Carrier Group

Colt military grade High Pressure tested and Magnetic Particle Inspected carrier and bolt.  Military grade staked gas port.  Test fired for tested.  Bolt is normally marked MPC.  The actual bolt may be marked with a "C" or might not be, depending upon what Colt is sending when your upper is assembled.


Upper Rail / Hand Guard       

Geissele Mk16 10.5" military grade upper receiver, roll marked "Geissele 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 4-prong Fast Attach Flash Hider (215-A), Surefire SOCOM 3-prong or Surefire SOCOM Close Time Surefire SOCOM 4-prong or Surefire SOCOM Warcomp 3-prong expertly timed and secured with Rocksett.  Note:  we time the Warcomp in Neutral position.  If you prefer the partially offset gas port, just let us know i the comments.

Note:  1)  The Warcomp could be a bit much for an 11.5", as significant blast will project through the ports.  Not well suited for indoor ranges, as you will make a lot of noise for your neighbor, but the Warcomp is still very popular.  2)  There are two different 4-Prong flash hiders.  The Fast Attach 215-A s a very attractive option, but is not compatible with current production SOCOM suppressors.  The other is a SOCOM compatible flash hider, but considerably more expensive.


 Gas Block

Standard is a Colt low profile factory installed and pinned gas block.  This is like an A-frame front sight base, but with the top removed, and two taper pins hold this in place.

Also available at no additional cost is the Sadlak extended gas block, steel constructed and phosphated coated and set in place with two set screws and the barrel dimpled to lock the set screws in place.  This is a good option, as the longer nose gas block will cover the front taper pin groove, from where the FSB was removed.

A Mk12 gas block is available as an option without additional fee.  Like the Sadlak extended gas block, the Mk12 gas block is set in place with bottom set screws and red Loctite, just like the US Navy SEALS used for two decades.  The Mk12 gas block is the most "military clone correct" of all the options.

Also, you may upgrade (for an additional cost) a Geissele Super Gas Block, black oxide or nitride blackened, and set in place with lower set screws and an additional drilling of a pin through the barrel.  


 Charging Handle

PRI gas buster charging handle, M84 with military latch. 

You may also upgrade to a Geissele Black Military Airborne charging handle, for an additional cost.  Contact our sales team for more information.


 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 military ammo recommended, but the 11.5" barrel is very tolerant of different ammo