The CMMG 16.1-inch 5.56 Carbine Barrel Sub-Assembly, M4 Profile (brand part no. 55DE10A) is ideal for building a custom AR-15 upper group and is sized to drop into a standard mil-spec AR-15 upper build. CMMG machines it from 4140 chromoly steel with a black nitride finish, cuts it to the classic M4 profile contour, and pairs it with a carbine-length gas system for a familiar, reliable recoil impulse. It ships with the M4 barrel extension already properly installed, saving builders a separate fitting step. For builders who want the standard, proven M4 contour on a fresh 5.56 upper, this AR barrel is ready to install.

Key Specifications

• Chambered in 5.56x45mm NATO.
• Barrel length measures 16.1 inches.
• Rifling twist is 1:7.
• Finished with a black nitride coating for corrosion resistance.
• Machined from 4140 chromoly steel.
• Built with a carbine-length gas system.
• Cut in the classic M4 profile contour.
• Ships with the M4 barrel extension properly installed.
• Sized to drop into a standard mil-spec AR-15 upper build.

Frequently Asked Questions

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

What gas system does this barrel use? A carbine-length gas system, matched to the 16.1-inch M4-profile barrel.

Buy the CMMG 16.1in 5.56 Carbine Barrel Sub-Assembly, M4 Profile

A pre-installed extension and the classic M4 contour give builders a straightforward, proven foundation for a general-purpose 5.56 upper. Order it from our Lubbock, Texas gun shop for fast, insured shipping.