Mk18 Mod 0 "Near Clone" CQBR Upper Receiver Group with TROY Quad Rail from Potomac Armory

The Mk18 Mod 0 "near clone" CQBR upper receiver group with Troy M4 RAS quad rail — assembled by Potomac Armory exclusively for Charlie's Custom Clones, built on a Colt 10.3" barrel.

• Near-clone Mk18 Mod 0 configuration: Colt 10.3" Crane-spec barrel, A-frame FSB, Troy M4 RAS quad rail, PRI Gas Buster charging handle
• Colt barrel, cut to 10.3": factory 14.5" barrel cut and re-crowned to 10.3" with 0.070" gas port — replicating how the first CQBR barrels were made by Navy armorers at NSWC Crane
• Chrome-lined and phosphated BCG: Carpenter 158 bolt, MPI inspected, staked gas key — selected for reliability under rapid fire and suppressed conditions
• Potomac Armory CAGE Code upper: 7075-T6 aluminum, M4 feed ramps, hardcoat anodized, T-marks, dry film lubricant

The Mk18 Mod 0 traces its origin to the Close Quarter Battle Receiver (CQBR) program, developed by the US Navy for SEAL teams and fielded through Naval Surface Warfare Center Crane. The original Mod 0 configuration featured a 10.3" barrel — created by cutting down standard Colt 14.5" M4 barrels — with a fixed A-frame front sight base and a quad rail. The CQBR designation refers specifically to the upper receiver group; "Mk18" is the full weapons system designation used primarily by the Navy and Marines. Army units commonly referred to the same short-barreled upper as the M4A1 Block 1 CQBR.

This is a "near clone" build — it uses a Troy M4 RAS quad rail rather than the program-spec KAC M4 RAS. Troy is a respected AR-15 parts manufacturer with a long production history, and the Troy RAS provides the same form factor and rail dimensions as the original KAC unit at a lower price point. For builders who want to enter the clone rifle space without the cost of all-original KAC components, the near-clone approach balances authenticity with budget.

Specifications

• Upper receiver: Mil-spec M4, 7075-T6 aluminum, hardcoat anodized, M4 feed ramps, Potomac Armory CAGE Code
• Barrel: Colt 10.3" (cut from 14.5"), chrome-lined, carbine-length gas, 0.070" gas port
• Front sight base: Colt "F" height A-frame, factory taper-pinned
• Rail: Troy M4 RAS quad rail with mil-spec ribbed rail guards
• BCG: chrome-lined and phosphated, Carpenter 158 bolt, MPI inspected
• Charging handle: PRI M84 Gas Buster, Mil Big Latch
• Rear sight: Magpul MBUS Gen 2 (upgradeable)
• Muzzle device: mil-spec A2 flash hider (suppressor-compatible with swap)

We assemble these with Potomac Armory to a standard that holds up under hard use. To complete your CQBR or Mk18 build, Charlie's stocks Mk18 Mod 0 lowers and the mil-spec vertical grip as well. Order yours today — we'll get it squared away.

All NFA laws apply. If building as an SBR, verify compliance with federal and state regulations before assembly.

* Photos show Knights Armament rail covers; product ships with PAT mil-spec ribbed rail covers. KAC 11-rib rail cover upgrades are available here.