HM 5.56 NATO Upper, 16″ Barrel, 10 3/8″ M-LOK, Black

Product Description

The HM 5.56 NATO Upper is a complete upper receiver assembly chambered in 5.56 NATO with a 16-inch barrel and a 10 3/8-inch M-LOK handguard in black.

This upper fits any mil-spec AR-15 lower receiver. It ships as a complete assembly, so you can attach it to your lower and head to the range.

The 16-inch barrel length is the most common choice for 5.56 NATO rifles because it balances velocity, handling, and legal considerations without requiring NFA paperwork.

Key Facts

• SKU: HM16MBUP-556
• Caliber: 5.56 NATO
• Barrel Length: 16 inches
• Handguard: 10 3/8″ M-LOK, black

Why a 16-Inch Barrel for 5.56 NATO

A 16-inch barrel is the shortest you can go on a rifle without entering NFA territory. It gives 5.56 NATO enough dwell time to cycle reliably while keeping the overall package maneuverable.

The M-LOK slots on the handguard let you mount lights, grips, and sling adapters without adding bulk. You get accessory flexibility where you need it and a slim profile where you don’t.

Compatibility with AR-15 Lower Receivers

This upper mates with any mil-spec AR-15 lower. The takedown pins, pivot pin, and charging handle interface are all standard-dimension.

If you already own a registered lower or you’re building a rifle from parts, this upper drops right on. No fitting or modification required.

What to Confirm Before You Order

Thread pitch, twist rate, gas system length, and barrel profile are not listed in the product name. Send us a message to confirm these specs if they matter for your build or intended use.

If you’re planning to suppress this upper or need a specific muzzle device, knowing the thread pitch ahead of time saves you a trip to the gunsmith.

Ordering from Western Sport

Order online and it ships straight to your door. Western Sport has been a licensed FFL/SOT dealer since 2007, and everything we sell carries the full manufacturer warranty. Questions before you order? Send us a message.

Frequently Asked Questions

Will this HM 5.56 NATO upper fit my AR-15 lower?

Yes, this upper fits any mil-spec AR-15 lower receiver. The pins and charging handle interface use standard AR-15 dimensions, so no modification is needed.

What is the difference between 5.56 NATO and .223 Remington?

5.56 NATO operates at higher chamber pressure than .223 Remington. A 5.56 NATO chamber safely fires both 5.56 and .223 ammunition, but a .223-only chamber should not fire 5.56 NATO.

Does the 16-inch barrel length require any NFA paperwork?

No, a 16-inch barrel does not require ATF approval or a tax stamp. Rifles with barrels 16 inches or longer are not regulated under the National Firearms Act.

What accessories can I mount to the M-LOK handguard?

M-LOK slots accept lights, vertical grips, hand stops, bipods, and sling mounts made for the M-LOK standard. You attach accessories with M-LOK-compatible hardware at any slot position.

How do I transfer a complete upper receiver in Texas?

A complete upper receiver is not a firearm under federal law and does not require an FFL transfer. You can order it and have it shipped, or pick it up in person at Western Sport.

Can Lance Rankin install a muzzle device or other parts on this upper?

Yes, Western Sport offers gunsmithing services on site. Send us a message to discuss muzzle device installation, sight installation, or other work you’d like done before you pick up the upper.

Additional information