The CMMG 12.5-inch 5.56 Multi Role Barrel Sub-Assembly (brand part no. 55DDF0A) is built for shooters assembling a custom AR-15 upper in a compact, carbine-length configuration. CMMG chambers it for the 5.56x45mm NATO round in the Multi Role profile, machines it from 4140 chrome moly steel, and applies a salt bath nitride finish inside and out for corrosion resistance. The barrel ships with the M4 barrel extension already installed and properly headspaced, so builders skip a separate gunsmithing step, and it uses a carbine-length gas system with a 0.750-inch gas journal. For builders assembling a compact upper, this AR15 parts selection includes this ready-to-install barrel sub-assembly.

Key Specifications

• Chambered in 5.56x45mm NATO.
• Barrel length measures 12.5 inches, a compact configuration.
• Built in the Multi Role profile, a versatile contour for general-purpose builds.
• Machined from 4140 chrome moly steel for strength and durability.
• Finished with a salt bath nitride coating inside and out for corrosion resistance.
• Rifling twist is 1:7, stable with heavier 5.56 bullet weights.
• The muzzle is threaded 1/2-28.
• Uses a carbine-length gas system with a 0.750-inch gas journal.
• Ships with the M4 barrel extension pre-installed and properly headspaced.

Frequently Asked Questions

Does this barrel come headspaced? Yes, it ships with the M4 barrel extension properly installed and headspaced.

Can this barrel go on a standard rifle-configured lower? No, at 12.5 inches it is under the federal 16-inch rifle minimum; it must go on an NFA-registered SBR or a pistol-configured upper without a shoulder stock.

What gas block does this barrel need? A 0.750-inch gas block matched to the carbine-length gas system.

Buy the CMMG 12.5in 5.56 Multi Role Barrel Sub-Assembly

A headspaced, ready-to-install barrel sub-assembly lets builders finish a compact 5.56 upper without a separate trip to the gunsmith. Order it from our Lubbock, Texas gun shop for fast, insured shipping.