Daniel Defense M4 FSP - Mk18 Style 10.3" Upper Receiver Group - NOS

A limited-production Daniel Defense M4 FSP upper receiver group — DD's 9.5" free-floating FSP rail system (DD1002) paired with a Colt 10.3" Mk18-configured barrel, assembled by Charlie's in partnership with Potomac Armory. New old stock from the early-2000s DD production run, limited to three units total.

• Rare Daniel Defense DD1002 rail: the 9.5" free-floating FSP rail, a screw-on RAS-style rail, not the modern RIS-II clamp-on design.
• Colt 10.3" Mk18 "Crane" barrel: Colt factory barrel cut down and reconfigured by Compass Lake Engineering with the gas port opened to 0.070" and re-crowned, phosphated 4150 chrome-lined, 1:7 twist, 5.56 NATO.
• Mil-spec forged upper receiver with M4 feedramps (no T-marks), Type III hardcoat anodized.
• Mil-spec nitrided BCG: 9310 MPI bolt, 8620 tool-grade carrier, staked gas key.
• PRI M84 Gas Buster charging handle and Magpul MBUS Gen 2 rear folding BUIS.

Daniel Defense's DD1002 FSP rail is one of the least-seen pieces of GWOT-era AR hardware. Dating to approximately 2005, it was produced in small numbers and discontinued when DD's product line moved toward the RIS-II and later the MFR/RIS-III platforms. The rail is a screw-on design over a front sight post, not the clamp-on, quick-detach RIS-II that most Mk18 clone builders are familiar with. It sits in a nostalgic middle ground: close to the Mk18 Mod 1 FSP configuration that has circulated in period photographs, but with a different attachment method and a different part number, and not known to have been widely fielded under any specific unit designation. Whether these rails saw limited prototype use during the GWOT build-up or were a commercial experiment that did not land is not documented in CCC's references — so this listing is honest about it.

Charlie's acquired the rail in factory DD boxes in new, unused condition and paired it with a Colt 10.3" barrel reconfigured by Compass Lake Engineering to Mk18 Crane specification — Colt factory chrome-lined chrome-moly steel barrel, factory Colt FSP installed, barrel cut down and re-crowned by CLE with the gas port opened to 0.070" (the Crane-spec port size for the 10.3" barrel). A Colt A2 flash hider is installed with a crush washer, properly timed. The upper receiver is a mil-spec forged M4 upper without T-marks, anodized to Type III hardcoat black, with M4 feedramps that mate to the Colt barrel extension. The BCG is a mil-spec nitrided complete group; the charging handle is the PRI M84 Gas Buster, as fielded on the Mk18 for suppressed use.

Specifications:

• Rail: Daniel Defense M4 FSP 9.5" free-float (DD1002), new old stock
• Barrel: Colt 10.3" chrome-lined, 1:7 twist, 5.56 NATO — CLE-reconfigured to Mk18 Crane spec with 0.070" gas port
• Muzzle device: Colt A2 flash hider, timed, crush washer
• Upper receiver: Mil-spec forged M4, no T-marks, Type III hardcoat anodized, M4 feedramps
• BCG: Mil-spec nitrided; 9310 MPI bolt; 8620 tool-grade carrier; staked gas key
• Charging handle: PRI M84 Gas Buster
• Rear sight: Magpul MBUS Gen 2 folding BUIS
• Production run: Three (3) units total

This is a one-and-done run. Daniel Defense has not re-introduced the DD1002 FSP rail and is not expected to. We keep the oddball clone-correct hardware when we can find it, and we don't restock what the factories won't. Copy that — grab one while they're here. 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.