At Charlie's Custom Clones, we have nick-named this upper the Block 1, Rev A. This is our nomenclature to show the free floating RAS upgrade, it is not an official military designation.
The M4A1 Upper Receiver Group is in Block 1 form, with an upgraded free floating RAS. The original M4A1 SOCOM upper receiver group had a standard KAC M4 clip-in RAS. Later in the Global War on Terror, Knights Armament upgraded their rail system to a free floating rail, or RAS. The free floating RAS allows the shooter to fully utilize the handguard rail without adding pressure to the barrel, and thus increasing accuracy. This M4A1 URG includes a Knights Armament forward vertical grip (VFG) and two full Knights Armament RAS 11-rib side rail panels and a smaller 6 rib lower rail panel to fit with the vertical grip.
The upper receiver is a Colt factory new, 7075 mil spec hard coat anodized complete with M4 feedramps, white top T-markings, keyhole forging from Cerro Fabricated Products (Cerro Forge) and mil-spec dry lube in the interior. These receivers do not have a Colt CAGE Code. 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. Not sure why, but the feedback we got from many of our customers was they preferred the keyhole marked uppers, so we are featuring Cerro forging with this upper receiver group.
The barrel is a Colt factory assembled 14.5" SOCOM profile barrel with Colt factory installed "F" height front sight post, chrome lined military grade 1:7 twist 5.56 NATO, high pressure tested and magnetically particle inspected barrel. An extended A2 flash hider has been installed by one of the best pin and weld shops in the US. Most of our customer never find the weld spot, as it is that good. We have also installed a factory new Colt front side sling swivel, as is standard for SOCOM issued barrels. the barrel is Colt CAGE Code marked and the exterior is mil-spec phosphated and oiled.
Bolt carrier group is 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). Charging handle is military grade forged black anodized aluminum.
A Magpul MBUS Gen2 rear back-up sight is standard.
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.
The M4A1 SOCOM upper receiver group is assembled for us by Potomac Armory. While this is a standard stocked item, most upper receivers are made as ordered, so please allow for some time for your upper receiver to be assembled. Also, while the mil-spec A2 extended birdcage flash hider is standard, other flash hiders can be ordered, for an additional cost and added time to build. Each barrel that is pinned and welded is sent out to a specialty fabrication shop in batches, so if you desire a Surefire or KAC or other muzzle device, your order will go with the next batch, adding a few weeks to the normal order time.
M4A1 SOCOM Complete Upper Assembly, Block 1, Rev A
Note: Standard configuration is NOT an NFA item. If you choose an unpinned barrel, all NFA laws will apply.
Note: All ITAR regulations apply. Charlie's deals in the real McCoy. Your item most likely has parts that cannot be shipped outside the USA, or owned in the USA by non-US Persons. You take accountability to safeguard parts and the entire upper, and get necessary approvals to transport outside the USA.
* Some Colt uppers are being shipped with the front sight base (FSB) not being marked with an "F" and the bolt carrier not being marked with a "C." All bolts are marked "MPC" like you would expect.