FAXON DUTY SERIES 14.5" M4 5.56 BARRELED UPPER

AR15 Upper Receivers › Barreled Uppers › 14.5″ M4 5.56  |  Works with: Mil-spec AR15 lowers • 5.56 BCG • 1/2x28 muzzle devices • 5.56 suppressors

Why a 14.5″ M4

The 14.5″ M4 is the reference carbine for a reason. It is short enough to handle in a vehicle or a hallway, long enough to keep 5.56 velocity useful, and its carbine-length gas system is matched to that barrel length. The M4 profile carries a heavier section behind the gas block for heat and a cut for the M203 mount ahead of it — the shape everyone recognizes.

The 1:7 twist is the military standard, chosen to stabilize long tracer and heavy projectiles; it shoots 55 gr ball just as happily.

Built on the Combat Series Barrel

This upper uses Faxon’s Combat Series M4 barrel rather than a nitrided Duty Series barrel. Combat Series barrels are 4150 CMV with a hard chrome-lined bore and a manganese phosphate exterior — the classic mil-spec construction for extreme round counts. Each barrel is stress relieved, air-gauge tested, MPI inspected, and headspace verified.

What’s in the Box

Also in the box: chamber flag, owner’s manual, and warranty registration card.

Bill of Materials

The exact Faxon parts this upper is assembled from, so you can check fitment, plan upgrades, or order a spare.

Build It Out

Faxon parts that fit this upper.

14.5″ M4 5.56 Upper FAQs

Is this barrel chrome-lined or nitrided?

Chrome-lined. The installed barrel is Faxon’s Combat Series M4: 4150 CMV with a hard chrome-lined bore and a manganese phosphate exterior, the classic mil-spec construction.

What twist rate is it, and what bullets does it like?

1:7, the military standard. It stabilizes 55 gr ball through 77 gr match and heavier projectiles.

Can I put it on a rifle lower?

Only if that lower is registered as a short-barreled rifle. A 14.5″ barrel on a lower with a stock is an SBR under the National Firearms Act. The installed A2 is threaded, not pinned and welded; a gunsmith can permanently attach a muzzle device long enough to bring the barrel to 16″ or more. On a pistol lower it builds an AR pistol. Check your state and local law.

What gas block and gas tube are installed?

A Faxon fixed .750″ 3-screw low-profile gas block on the 1.9″ journal, with a carbine-length gas tube.

Does it include a bolt carrier group and charging handle?

No. Add a standard 5.56 BCG and charging handle. The complete version ships with both installed.

Will it run a suppressor?

Yes. The 1/2x28 muzzle takes 5.56 direct-thread cans and mounts once the A2 is removed, or a 1/2x28 HUB adapter.

Where is it made, and what is the warranty?

Assembled by Faxon in Greater Cincinnati, Ohio, and covered by the Faxon Lifetime Guarantee.

Barrel figures are from the Combat Series barrel’s published specifications; weight is for the barrel alone. Components are listed from the Faxon build sheet for this SKU. Lower receiver, buffer, and magazines sold separately. Covered by the Faxon Lifetime Guarantee.