Geissele Mk13 10.3" Chop Boss Special Upper Receiver Group

One of our Limited Production Custom Mk18-ish upper receiver groups from Chop Boss and Potomac Armory

What do you get when you put the alphabet soup of military short barreled upper receiver groups together with the Mk-whatever alphabet soup of Geissele's rails and mix it with the custom made chop rails from Chop Boss, and throw it into a 10.3" package?  We're not sure either, but the end product kicks butt.  This is the result.  Is it a Mk18?  Sort of.  It is 10.3" of Colt Crane Mk18 barrel with a front sight base, with the Geissele Mk13 rail, and custom designed and assembled by Potomac Armory with the Chop Boss innovating with a Geissele Mk13 rail to accommodate the front sight base.

Confused yet?  Don't worry.  Charlie's Custom Clones has you covered.  We are not exactly sure why every rail that Geissele builds has to have a "Mark" name in it, and it just so happens that every "Mark rail" has absolutely nothing to do with the "Mark" that exists in the US Navy.  Well, the Geissele Mk13 is a discontinued rail, so however excited we all will be with the Chop Boss's magic in creating this FSP version of a Mk13 rail, Potomac Armory has built us a super cool custom 10.3" upper receiver group.

Okay, so by now, you are following along.  Geissele Mk13 rail in 9.5".  Chop Boss does his magic and cuts the rail open to accommodate a front sight post.  Now, add a Colt military spec Mk18 barrel in 10.3" with a front sight base.  Swizzle in a mil-spec forged upper receiver, anodized black, a Geissele Super Charging Handle in black, a black nitrided, mil-spec M16 bolt carrier group, and throw-in a Magpul MBUS Gen2 rear sight, and you begin to feel the magic.

Highlights

• Geissele Mk13 rail at 9.5" custom cut by Chop Boss to fit a front sight post.
• 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 forged upper receiver with 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.
• Geissele Super Charging handle, in black.
• Magpul MBUS Gen 2 rear back up folding sight.

So what else do you need to know?  Well, Charlie's loves to bring you strong quality made products, and this one is very unique.  Chop Boss is seen on Instagram, where he has created quite a following doing... well... chopping perfectly good rails into smaller parts.  He is quite the craftsman, and Charlie's loves to highlight the work of American craftsmen.  The Colt barrel, by the way, is military grade and will outlive all of us.  Quality through and through, and made in the same way that NSWC Crane made the Mk18 barrels for the US Navy in the early 2000s during the Global War on Terror.  Geissele, well you know them.  Nothing but the best.

We hope you enjoy this limited edition short barreled upper for your SBR or pistol build.