Centurion Arms Mk12 Complete Upper, 12.5" 5.56mm, Stainless Match Barrel, Quad Rail

Centurion Arms 12.5" Custom Mk12 style RECCE Upper Receiver Group

Centurion Arms kept what made the Mk12 shoot, the stainless match barrel and the brake-and-collar muzzle, and took five and a half inches off the front. This is the complete upper for the builder who wants that barrel and that muzzle in a build that handles like a carbine.

Why the Mk12 still matters

The Mk12 Special Purpose Rifle program took shape at Naval Surface Warfare Center Crane around 2000. The recipe was an 18-inch stainless match barrel, a free-floated handguard, heavy 77-grain match ammunition and the OPS Inc. 12th Model suppressor riding on a brake and collar. It gave a small team 5.56mm precision well past the practical reach of an M4, and it served across the Global War on Terror.

It was also long. Add the suppressor and it was longer still.

The same recipe at 12.5 inches

Centurion keeps the parts that made the rifle shoot and shortens the rest. The barrel is stainless and match grade. It is air-gauged, which means the bore is checked for the same diameter from end to end. It is chambered in 5.56mm with the 1:7 twist the Mk12 used for its 77-grain match load, and it runs a carbine-length gas system. Centurion says its barrels need no break-in, so you can mount your optic and go zero it.

Pinned gas block, free-float C4 quad rail

Centurion's founder, Monty LeClair, is a retired Navy SEAL with a sniper background and Mk12 experience. Most Mk12 gas blocks are not pinned. Centurion pins this one to the barrel, so it stays put when the barrel gets hot.

The receiver is a forged mil-spec upper with polished M4 extended feed ramps. A 7-inch Centurion C4 quad rail free-floats the barrel, so nothing you hang on the rail touches it, and gives you Picatinny rail on four sides for a light, a laser and a bipod.

Brake and collar, ready for the AEM5 suppressor

Out front is Centurion's own OPS Inc. pattern brake and collar, the detail that makes a Mk12 look like a Mk12. Run it bare and the brake cuts recoil.

The 12th Model suppressor is carried on today as the Allen Engineering AEM5. It threads onto the brake, and its rear seats on the collar. Because it slides back over the barrel, it adds less length than a suppressor that hangs off the muzzle. That answers the length problem twice: a shorter barrel, and a suppressor that sits back over it.

Is it right for your build?

Yes, if you want:

• a short, accurate upper with the Mk12's barrel and muzzle
• a host for an AEM5 suppressor
• the short one you reach for when the 18-inch Mk12 stays in the safe

No, if you are building a clone-correct Mk12 Mod 0 or Mod 1. Those rifles ran 18-inch barrels on rifle-length gas, and the rail here is Centurion's own C4, not the Precision Reflex (PRI) carbon fiber handguard of the Mod 0 or the Knight's Armament (KAC) free float rifle rail, KM21318, of the Mod 1.

A shorter barrel also gives up velocity, and with it some reach. If a faithful clone is the goal, start with our Mk12 Mod 0 or Mk12 Mod 1 rifle.

Ships without bolt carrier group, charging handle, sights or optic.

Choose above:

• Ready to ship: on our shelf, ships in 3 to 7 days
• Built as ordered: built for you by Centurion, 3 to 8 weeks

What's in the box

• forged upper receiver
• 12.5-inch stainless match barrel
• pinned low-profile gas block
• 7-inch C4 quad rail
• Centurion OPS Inc. pattern brake and collar

Finish it your way

Add a bolt carrier group and a good scope, and the Mk12's barrel and muzzle go wherever you do. Charlie's would be proud to send you one.

Specifications

Further reading: The Mk12 and the OPS Inc / AEM5 Suppressor Evolution

This upper is sold as a part. Put it on a rifle lower and the finished rifle is a short-barreled rifle (SBR) under the National Firearms Act (NFA).