The MMR-556-20 is our 20 inch barreled variant of the MMR-556. These rifles are built to be the functional tool that the end user needs to meet and overcome any challenge.

At the heart of our rifles, we use our M16 cut nitride bolt carrier group, matched with a fully nitrided Ballistic Advantage 20” rifle-length barrel. Our rifle-length gas system provides an extremely soft and controllable recoil impulse. We then paired these components with our tight fitting receivers, and ultra-rigid 15” M-LOK rail system to provide a rifle that is up for any task.

Our 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. Our fitted disconnector gives a positive, short reset that is hard to miss!

2 in stock


2 in stock

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

• Rifle length buffer tube, Rifle Buffer, Stainless Steel Spring

• Magpul MOE Rifle 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


•Custombilt 15” MLOK handguard,Hard-Coat Anodized Mil 8625 Type 3 Class 2 – Matte Black


• 20″ Barrel (1:7 twist)

• 4150 Chrome Moly Vanadium

• Nitride/QPQ Finish

• Thread: 1/2 x 28

• A2 Flash Hider

• Low profile 4140 nitride gas block

• Rifle- 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

• 9310 Bolt

• 8620 Bolt Carrier