CMMG .308/7.62x51mm MK3 3GR AR-Style 18″ Complete Upper (38BCCE5)

CMMG .308/7.62x51mm MK3 3GR AR-Style 18″ Complete Upper (38BCCE5)


2 in stock

SKU: CMMG38BCCE5 Categories: ,

The CMMG MK3 3GR complete upper receiver is CMMG’s solution to the heavy-metal class in 3-Gun matches. Although this upper was originally designed for competition, due to its excellent balance, comfortable features and high reliability, this upper is well suited for any situation the requires accurate hits in a limited amount of time.



The heart of any AR-10 style rifle is the barrel. CMMG is not spared any expense in building this match grade .308 upper receiver. The barrel used in this upper is precision machined from 416 stainless steel. This high grade stainless steel is an excellent barrel material and will ensure optimal accuracy.

The barrel is 18” in length. This intermediate barrel length is truly optimal for the .308/7.62x51mm cartridge. The 18” barrel length keeps the overall length of the your rifle down while still allowing adequate length to get a good powder burn to ensure high bullet velocities. This allows you to be able to swing the rifle around quickly, but still be able to reach to to long range targets without a rainbow like trajectory that shorter barrels would give you.

The barrel has a heavy taper profile. This heavy taper give the barrel more mass. Since the barrel has more mass, it will be better able to dissipate heat which can prevent heat related accuracy issues. The heavy profile can also have the effect of reducing felt recoil. Due to the increased mass, the rifle will be less likely to move from its resting position. This can help you to stay on target longer for faster follow up shots.

The barrel is chambered in .308 winchester. With this chambering dimension, you will be able to safely shoot both .308 Winchester, as well as 7.62x51mm NATO ammunition. The barrel has a rife length gas system.

The barrel has a 1:10 twist rate and has a bead blasted stainless steel finish


Muzzle Device

The MK3 3GR upper receiver comes with CMMG’s SV muzzle brake. This brake features laterally facing ports to decreases felt recoil. The brake also has upward facing vents. These upward facing vents help to control muzzle rise in order to allow you to stay on target and get fast follow-up shots. If you are looking to put a lot of rounds on target, this muzzle brake will help you to accomplish that.



The CMMG 308 upper comes complete with RKM15 hand guards. This handguard has three full length sections of keymod accessory attachment slots. These keymod slots allow you to attach any of your compatible keymod accessories. The 12 o’clock section of the handguard features a full length picatinny rail section this allows you to mount all sorts of optics. You can also mount back-up or offset iron sights.



The receiver for this complete upper is precision machined from 6061-T6 aluminum. The receiver is patterned after the LR308 and will fit DPMS style lower receivers.  

Additional information

Weight7.5 lbs
Part #



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