Faxon Firearms Ion Fx5500U Ultlght 556 16 Upper

The Faxon Firearms Ion FX5500U is a complete 5.56 NATO upper receiver built for shooters who refuse to compromise on weight without sacrificing durability. If you're running a short-barreled AR platform and want to shed serious ounces without cutting corners on rigidity or reliability, this upper receiver strips roughly a pound off a standard build while keeping everything that makes an AR-15 run hard. It's the kind of upper you bolt on, shoot, and forget about—because it just works.

At the core is Faxon's 14.5" pencil barrel paired with an integral slim 3-port muzzle brake, engineered to meet NFA 16" minimum barrel length requirements. The thin profile keeps rotational inertia down and cooling efficient. Topping it is a 13" carbon fiber M-LOK handguard designed for the Streamline platform—stiff, lightweight, and modular enough for your optics, lights, and sling hardware. The handguard and pencil barrel combination create a sleek platform that doesn't feel over-built for what you're trying to accomplish.

The bolt carrier group is Faxon's own lightweight design, engineered to cycle reliably while dropping unnecessary mass. A multi-position adjustable gas block lets you tune the action to your ammunition and shooting style, and the enhanced ambi charging handle works either shoulder. Everything is housed in a Faxon Enhanced Forged upper receiver—the foundation that ties it all together.

Total weight sits at 3.1 lbs, a meaningful reduction if you're building a duty, competition, or general-purpose rifle where every bit counts. Drop two pins into your lower receiver and you've got a complete upper ready to run.

Key Features

• 14.5" pencil barrel with integral slim 3-port muzzle brake (NFA-compliant 16" equivalent)
• 13" carbon fiber M-LOK handguard—lightweight and rigid
• Faxon Gunner lightweight bolt carrier group for reduced reciprocating mass
• Multi-position adjustable gas block for ammo and duty tuning
• Enhanced ambi charging handle for both-side operation
• Faxon Enhanced Forged upper receiver
• Total weight: 3.1 lbs

Specifications

Frequently Asked Questions

What lower receiver will this upper fit?

This is a standard AR-15 upper receiver that will pin to any mil-spec AR-15 lower. You supply the lower; the upper and lower connect with two takedown pins.

Does this upper meet short-barrel rifle (SBR) or NFA requirements?

The barrel is 14.5" with an integral muzzle brake that brings the total to 16", meeting NFA minimum barrel length requirements for a rifle configuration. Always verify compliance with your local and federal regulations before assembly.

What's included in this upper receiver?

The upper includes the forged upper receiver, 14.5" pencil barrel with integral muzzle brake, 13" carbon fiber M-LOK handguard, lightweight bolt carrier group, multi-position adjustable gas block, and enhanced ambi charging handle. You do not get a lower receiver, magazines, or ammunition.

Why choose a pencil barrel over a heavier profile?

Pencil barrels reduce overall weight and rotational inertia, making them popular for builds where weight savings matter—competition, duty, or lightweight hunting rigs. The trade-off is reduced thermal mass, so sustained rapid fire will heat the barrel faster than a heavy profile. This upper pairs a pencil barrel with an adjustable gas block, letting you manage recoil and reliability across different loads.