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Custombilt Firearms MFG MMRB-556 5.56 NATO Rifle - 16"

AR-15 Rifle


The MMRB rifle combines modern features with classic lines. The MMRB-556 contains the same components as the MMR-556, but incorporates an F marked front sight block, and Magpul Industries MLOK SL handguard. This combination results in a slightly more cost effective rifle that is still suited for extremely hard use. 

At the heart of their rifles, Custombilt use their M16 cut nitride bolt carrier group, matched with a fully nitrided Ballistic Advantage 16” mid-length barrel. Their mid-length gas system provides an extremely soft and controllable recoil impulse. 

Custombilt's MPP-GI trigger has micro polished contact surfaces, and a fitted disconnector. This combination gives you the 5lb weight of a typical duty trigger, and removes all of the gritty drag while breaking the shot. Their fitted disconnector gives a positive, short reset that is hard to miss!


Forged Lower Receiver:

  • 7075-T6 Forged Aluminum
  • Hard-Coat Anodized Mil 8625 Type 3 Class 2 - Matte Black
  • Upper Receiver Tension Screw with nylon tip to remove any slack between lower and upper receiver.
  • Detent Set Screw for rear take-down pin (captures spring that is normally held in by the end plate.)
  • Bolt Catch Screw (Used in place of the Bolt Catch roll pin)
  • Custombilt MPP Trigger: (Micro Polished Performance) GI Trigger
  • Custombilt Enhanced Trigger Guard
  • 6-Position Mil-Spec Buffer Tube, Carbine Buffer, Stainless Steel Spring
  • Magpul CTR Stock
  • Magpul MOE Grip
  • Mil-Spec Safety Selector
  • 30 round magazine


Forged Upper Receiver:

  • 7075-T6 Forged Aluminum
  • T-Marked Flat-Top with Picatinny Rails
  • Hard-Coat Anodized Mil 8625 Type 3 Class 2 - Matte Black
  • Mil-Spec Charging Handle



  • Magpul SL Handguard


Barrel (1:7 twist)

  • 16"
  • 4150 Chrome Moly Vanadium
  • Nitride/QPQ Finish
  • Thread: 1/2 x 28
  • A2 Flash Hider
  • Pinned Front Sight Block
  • Mid- Length Gas System


Custombilt M16 Bolt Carrier Group:

  • Properly staked gas key
  • Nitride Coated
  • Laser Engraved Custombilt Logo
  • HPT - High Pressure Tested
  • MPI - Magnetic Particle Inspected
  • 9130 Bolt
  • 8620 Bolt Carrier


Weight: 6.45 lbs

Includes: (1) Lancer 30rd Magazine

More Information
Product Type AR-15 Rifle
Manufacturer Custombilt Firearms MFG
Thread Pitch 1/2x28
Gas Length Mid
Barrel Length 16"
Caliber 5.56 NATO
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