Mk18 Mod 1 Upper Receiver Group, Military Special Edition

Charlie's Military Special Edition Mk18 Mod 1 upper receiver group — a clone-correct Naval Special Warfare 10.3" CQBR upper built on a genuine Colt M4 upper receiver with a Daniel Defense RIS-II rail in FDE, Colt BCG, and PRI Gas Buster charging handle.

• Clone-correct Mk18 Mod 1: built to the NSW Crane-issued configuration that replaced the Mk18 Mod 0 in the mid-2000s.
• Genuine Colt M4 upper receiver — mil-spec perfection, with interior white T-marks. CAGE-code or Cerro-forge options available on request.
• Daniel Defense RIS-II free-float rail in FDE: anodized FDE (not Cerakote), with period-correct FDE ladder rail covers.
• Colt complete bolt carrier group: C-158 steel bolt, MPI and HP-tested, tool-steel carrier with staked gas key, phosphated.
• PRI Gas Buster charging handle — the NSW-issued charging handle for suppressed Mk18 use.

The Mk18 Mod 1 is the shortest rifle system in the M4 family adopted by U.S. Naval Special Warfare. The original Mk18 was standardized at a 10.3" barrel in the early 2000s at NSWC Crane when armorers were asked how short the barrel could go while still supporting the NT4 suppressor and retaining the bayonet lug. The Mod 1 variant updated the Mod 0 by replacing the KAC RIS rail with the Daniel Defense RIS-II — a free-float, monolithic-top-rail design — and is the configuration most closely associated with GWOT-era NSW boarding and direct-action use.

This upper is built on a genuine Colt M4 upper receiver. Current Colt-forged uppers come from Cerro Forge (keyhole mark, no CAGE code) or Brass Aluminum Forging (square mark, CAGE-code marked); both are Colt, both carry interior white T-marks, and both are mil-spec. The CAGE-code marked receivers can have extended lead times, so builders who want a specific variant should ask before ordering. The Daniel Defense RIS-II is an anodized FDE — not Cerakoted — which is closer to the factory FDE rails used on Crane-issued Mk18 Mod 1 rifles. It ships with period-correct FDE ladder rail covers rather than the newer black covers Daniel Defense currently packages.

The Colt 10.3" barrel is the Mk18 program barrel — chrome-lined, 1:7 twist, chambered in 5.56 NATO, and supplied with the Colt front sight base (F-height) factory-timed and pinned. The Colt complete BCG is the same bolt carrier group Colt ships on contract rifles: C-158 bolt, MPI and HP tested, tool-steel carrier with staked gas key, phosphated finish. Some Colt carriers carry a "C" stamp on the carrier body and some are unmarked — both are identical in quality and test protocol. The PRI M84 Gas Buster charging handle is included as the last Crane-issued piece; it vents gas away from the shooter's face during suppressed fire, which is how Mk18s are usually employed.

Specifications:

• Upper receiver: Colt forged M4 (CAGE-code or Cerro, interior white T-marks)
• Barrel: Colt 10.3" SOCOM profile, 1:7 twist, chrome-lined, 5.56 NATO
• Gas system: Carbine length, with F-height FSB factory-pinned by Colt
• Rail: Daniel Defense RIS-II, anodized FDE, with FDE ladder covers
• BCG: Colt complete, C-158 bolt, MPI/HP tested, staked gas key
• Charging handle: PRI M84 Gas Buster
• Muzzle device: A2 flash hider (configurable to NT4-compatible on request)

This is the Mk18 Mod 1 upper as the U.S. Navy built it, not a silhouette match. We've got your six on the clone-correct details — from the Colt forging to the correct DD RIS-II shade to the PRI gas-buster. Order yours today and we'll square you away. This is an upper receiver group; it is not a serialized firearm and ships without an FFL. A 10.3" upper installed on a rifle lower requires an approved NFA Form 1 SBR tax stamp; on a pistol lower, no stamp is required under current law.