M4A1 SOPMOD Block 2 Upper Receiver, Military Special

$2,095.00 - $2,145.00
Assembled to Order, ships in 3 to 6 weeks, as pin and weld services will require additional time

Colt M4A1 SOPMOD Block 2 Upper Receiver, Military Special

Colt Receiver with Daniel Defense M4A1 RIS-II FDE rail



This is a custom-made M4A1 URG with a 14.5" pinned and welded barrel, with Surefire Warcomp SOCOM extended flash hider for an overall 16" non-NFA setup.

Charlie's Custom Clones offers the SOPMOD Block 2 in this configuration of the straight rail, and also the FSP with the front sight base.  Both are correct.

This is pretty much what you need for a true military correct clone build of the M4A1 Block 2 straight rail upper receiver group.  Like an aged Scotch Whisky or a fine Bordeaux red wine, this is a working museum piece.  Admire it, but shoot it.  Are you missing anything with this M4A1 upper?  Not really.  And, with the Warcomp flash hider, you are getting an upgrade from USGI period correct.  


  • Military Correct
  • Colt Upper Receiver
  • Daniel Defense RIS-II M4A1 Block 2 straight rail, with Mk12 gas block lower cutout and M203 grenade launcher tabs - in FDE
  • 14.5" military spec barrel:  Government profile, 5.56 NATO, 1:7, chrome-lined, Chrome-Moly steel alloy with phosphate exterior
  • Surefire SOCOM muzzle device, pinned for a 16" legal barrel (Your choice of Warcomp, 4-prong or brake)
  • Mk12 gas block - as used by military 20 years ago
  • KAC back-up iron sights (period correct) 
  • PRI M84 "gas buster" charging handle
  • Colt BCG

The US military chose the M4A1 as the standard rifle for special forces and infantry alike during the Global War on Terror in the Afghanistan and Iraq theaters in the early 2000's.  The Block 1 featured the shorter RAS rail from Knights Armament and 14-1/2" M4 barrel with a front sight post.  Later, as part of the SOPMOD upgrade program, the SOPMOD Block 2 was introduced, and offered a free floating rail from Daniel Defense.  The SOCOM barrel models would offer the ability to mount an M203 grenade launcher, while the M4 barrels generally did not support the grenade launcher.  In a Company of Infantry or a special forces unit, not every soldier needed the M203 grenade capability, and this model has a standard M4 barrel under the RIS rail system.

The M4A1 Upper Receiver Group is in SOPMOD Block 2 straight rail form, with an upgraded Surefire Warcomp muzzle device.  The original M4A1 SOPMOD rifles had the Surefire SOCOM 4-prong flash hider.  Newer versions of military weapons are upgrading the Warcomp on 14.5" barrels, which provide better performance, blending the flash hiding capability with the porting of a break to provide for a well-rounded blend of flash suppression and braking to mitigate recoil and muzzle rise.  The Daniel Defense RIS-II M4A1 rail is in traditional FDE with period correct FDE ladder rail covers.  The M4A1 RIS rail provides for additional Picatinny rail space for accessories like a Surefire flash light, a PEQ-2 or PEQ-15 night vision illuminator, and other accessories, all without burdening the M4 barrel, as the RIS rail is a free-floating rail system.  Daniel Defense provided RIS rails for the M4A1 straight rail, as well as the M4A1 SOPMOD Block 2 FSP and the Mk18 CQBR.

The upper receiver is a Colt factory new, 7075 mil spec hard coat anodized complete with M4 feedramps, white top T-markings, CAGE Code markings and mil-spec dry lube in the interior.  Beginning in late 2020, Colt started to make square forged (Brass Aluminum) CAGE Code and M4 marked uppers, and the Cerro Forged uppers without CAGE Code and without M4 markings above the gas tube port.  For the Military Special SOPMOD Block 2, Charlie's chose to use the Colt CAGE code marked upper receivers.

The barrel is a factory new 14.5" M4 Government profile barrel.  Charlie's Custom Clones, working with its design and build partner, Potomac Armory, is sourcing carbine gas system barrels, as per military spec, from Colt, FN and Daniel Defense, depending upon which manufacturer is able to meet our supply needs.  The Colt barrels often come with a pinned A-frame front sight base, and when that barrel is sourced, we have our barrel shops phosphate coat the barrels a second time to assure no corrosion from the front sight pin holes.  Our Military special M4A1 upper receiver groups are fitted with a Mk12 gas block, as was standard for the non-FSP SOPMOD Block 2 uppers.  The Daniel Defense RIS rail is specifically designed for the Mk12 gas block, originally designed by NAVSEA, for use on a carbine gas length barrel, and the Daniel Defense M4A1 rail has a opening at the bottom to accommodate the larger bottom portion of the Mk12 gas block.  The Mk12 gas block is secured by set screws in the bottom and locked in place with red Loctite, as was standard for USGI issued M4A1 uppers.  Barrels are chrome-lined 5.56 NATO chambered and are magnetic particle inspected and high pressure tested, with a mil-spec phosphate coated 4150 steel barrel.  All barrel manufacturers provide similar specifications in 1:7 twist, and all are used by the US military:  Colt, FN and Daniel Defense.

The barrel is finished with a Surefire SOCOM Warcomp muzzle device, which is pinned and welded in place by an outside shop that Charlie's and Potomac Armory which provides superior workmanship.  In fact, you might not even notice that the flash hider was welded.  The craftsmanship is that good!  Charlie's recommends what is known as "neutral timing" of the Surefire Warcomp.  This means that we "point" the gas ports upwards.  This is important to note, as Surefire actually recommends an off-center timing.  It is a preference, and we have found that most customers prefer the timing of the ports to be upward.  If you would like your Surefire Warcomp to be timed off-center, you just need to specify that to us.  There is no additional cost.  The Surefire SOCOM Warcomp is compatible with the Surefire SOCOM suppressor line, and Charlie's recommends the Surefire SOCOM RC2 in FDE, but we also offer the RC2 in black, in addition to Mini-2 SOCOM suppressors from Surefire, which also fit the Warcomp muzzle device.

Bolt carrier group is Colt M16 full auto mil-spec shot peened phosphated tool steel and chrome lined interior and chrome lined gas key hardened to USGI specifications and Grade hardened and staked fastener.  The bolt is mil spec Carpenter 158 steel, magnetic particle inspected (MPI).  Colt Bolts are typically marked "MPC" and the carrier may or may not be marked with a "C" as Colt provides carriers either way.  In past years, one could tell a Colt carrier by the "C" marking, but that is not always the case.  Charging handle is a PRI M84 "gas buster" charging handle, as used by the US military.

Knights Armament back-up sights are provided:  The original M4 folding front sight and the full sized 600 meter rear sight.

The barrel is pinned and welded to a length of 16", so the upper receiver can be installed on any standard M4 or AR15 lower receiver and be "street legal" without the need for registering as a short barreled rifle.

Built to Charlie's specifications by Potomac Armory.  Potomac Armory features Colt and Remcon North parts and gas tubes.


  • Accommodates the full range of 5.56mm ammunition, including the NATO M855/SS109 and U.S. M193, as well as longer-range ammo like the Mk262 Mod1 77 grain, preferred for SOCOM operations, utilizing a rifling twist of 1 turn in 7".
  • Colt forged and hard coat military spec anodized M4 upper receiver with CAGE Code and Brass Aluminum (square forge), M4 marked above the gas tube port and dry lube film inside the receiver.  T-marks on the top are painted white, per military spec.  Note that Colt produces battle rifles, and the finish of some Colt upper receivers will show handling marks and sometimes minor scratches
  • Mil-spec 14.5" M4 Government profile Carbine gas system barrel, chrome-lined, mil-spec phosphated exterior, 1:7 twist and 5.56 NATO chambered, MPI/HP from Daniel Defense, Colt or FN, as supplies permit
  • Colt M16 factory bolt carrier group with high pressure tested and magnetic particle inspected bolt and chrome lined carrier and gas key
  • Daniel Defense RIS-II M4A1 rail in factory anodized FDE with period correct Daniel Defense Ergo ladder rail covers (3 each)
  • Knights Armament (KAC) backup iron sights:  M4 folding black sight (part number 99051) and rear full-sized 600 meter folding rear sight (part number 98474)
  • Mil-spec Mk12 gas steel gas block, phosphated per mil spec from Daniel Defense, Badger Ordnance or Potomac Armory, as supplies permit
  • Surefire SOCOM Warcomp 5.56 muzzle device or Surefire 4-prong flash hider.  Standard is Warcomp, neutrally timed.  If you wish a different timing, we can do that with no additional cost.  Also, if you want the 4-prong, or if you live in a state, or jurisdiction, that does not permit flash hiders, we can substitute a Surefire muzzle brake at no extra charge. Just add a note in the comments to your order, when you check-out.
  • PRI M84 gas buster charging handle.

Pictures courtesy Potomac Armory and the US Department of Defense