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

Limited edition, small supply, all fully built. When in stock, ships in 3 to 4 days from our workshop
Extremely Limited Production:
rail is discontinued, once sold out, no more will be available

Old School Daniel Defense M4/Mk18 FSP Upper Receiver Group

Limited Production Free Floating Handguard with exposed front sight post.

Charlie's brings you a limited production Daniel Defense upper receiver group, featuring the 9.5" free floating M4 FSP Rail System. This is NOS, or "new old stock" rail. The rails come to us in new condition, factory Daniel Defense boxes. As best we can tell, the rail system dates back to around 2005 (+/-) and, in its time, was very limited production. The rail is similar to the DDMk18 FSP, but is not the RIS-II rail, but rather a screw-on RAS style rail. We have paired the rail with a mil-spec upper receiver and Colt 10.3" Crane Mk18 Mod 1 barrel. This setup is a variation on the Mk18 Mod 1 with FSP or front sight post, but is not the same rail that many know as the DD Mk18 FSP, but is a great looking piece of nostalgia with a super-rare rail.

Charlie's, working with Potomac Armory has produced only three (3) of these. After we sell out, there will be no more unless DD re-introduces this rail, which is not likely.

We do not know which units fielded this modified Mk18, or perhaps was a prototype that never got launched. During the big build-up of the Global War on Terror in the early 2000s, many variations of different weapons were prototyped, or used for one-off missions for special forces.


  • Daniel Defense M4 9.5" Free Floating FSP Rail (DD1002), New Old Stock
  • Colt factory barrel with Colt installed front sight post, cut down by Compass Lake Engineering to be a Mk18 "Crane" barrel, with the gas port opened up to 0.070" and re-crowned and phosphated 4140 Chrome-Moly Steel with factory chrome lining, 1:7 twist chambered in 5.56 NATO, factory installed M4 extension with feedramps topped with a Colt A2 flash hider, properly timed and mounted with crush washer.
  • Mil-spec M4 forged upper receiver without 'T' marks, hardcoat black Type III anodizing with M4 feedramps to marry-up with the Colt barrel extension.
  • Mil-spec nitrided Bolt Carrier Group with 9310 steel MPI bolt and 8620 tool-grade steel carrier, and staked gas key.
  • PRI M84 Gas Buster Charging Handle, as originally used on the Mk18.
  • Magpul MBUS Gen 2 rear back up folding sight.