FAXON DUTY SERIES 16" GUNNER 350 LEGEND COMPLETE UPPER

AR15 Upper Receivers › Complete Uppers › Duty Series 16″ 350 Legend

What’s on This Upper

Every major part is a Faxon part that is also sold on its own; each card links to its product page, specs, and reviews.

Not included: lower receiver, optic.

Barreled, Complete, or Suppressor Ready?

Faxon builds each upper in up to four configurations. A barreled upper has the receiver, barrel, gas system, handguard, and muzzle device installed, with no bolt carrier group or charging handle. A complete upper adds both, so it is ready to pin to a lower. Suppressor ready versions swap in a MuzzLok® Plan B compatible flash hider and, on gas guns, Faxon’s patented adjustable gas block, so a suppressor mounts with one adapter and the gas can be tuned to it. This one is the complete upper.

What a 350 Legend Upper Needs

350 Legend is a straight-wall .357 cartridge on the standard 5.56 bolt face. It runs in Faxon’s Big Bore upper, whose feed ramps and ejection port are opened up for big cases; feeding problems with 350 Legend usually come down to the magazine, so use 350 Legend magazines.

Want to Run a Suppressor Later?

The muzzle is threaded 1/2x28, so a direct-thread HUB adapter or any .36 cal muzzle-device mount works. For a suppressor that runs on and off the rifle, Faxon recommends adding a patented adjustable gas block to tune for the extra back-pressure. Or skip the parts list: the suppressor-ready version of this upper comes with both.

How It’s Built and Inspected

Finish the Rifle

This upper pins to any mil-spec AR-15 lower. Faxon makes three, all from 7075-T6 forgings with an upper-to-lower tensioning screw to take out receiver play. The lower is the serialized part, so it ships to an FFL; the upper doesn’t.

What Reviewers and Owners Say About These Parts

This upper is new, so it has few reviews of its own yet. Every major part on it is sold on its own, so here is what independent reviewers and Faxon customers have said about the barrel, carrier, handguard, gas block, and receiver.

Average ratings on FaxonFirearms.com, out of 5 stars: 16″ Gunner 350 Legend barrel: 5.0; BCG: 4.9; handguard: 4.8; gas block: 4.7; muzzle device: 5.0.

Compare the Duty Series 16″ 350 Legend Uppers

Duty Series 16″ 350 Legend Complete Upper FAQs

What comes on this upper, and what doesn’t?

Included: Enhanced Forged Big Bore upper, 16″ Duty Series Gunner 350 Legend barrel, 15″ Streamline aluminum M-LOK handguard, fixed .750" low-profile gas block, carbine-length stainless gas tube, 9mm A2 flash hider, Superfinished 5.56 M16 BCG, nitride, mil-spec AR-15 charging handle. Not included: lower receiver, optic.

What’s the difference between a barreled upper and a complete upper?

A barreled upper has the receiver, barrel, gas system, handguard, and muzzle device installed but no bolt carrier group or charging handle. A complete upper includes both and is ready to pin to a lower. Suppressor-ready versions add a MuzzLok® Plan B compatible flash hider and Faxon’s patented adjustable gas block.

Will this upper fit my lower?

Yes, if it’s a mil-spec AR-15 lower. Mil-spec uppers and lowers share the same pin locations and dimensions. Billet receivers from different makers can fit tighter or looser; Faxon lowers include a tensioning screw to take out play. AR-10, AR-9, and dedicated-lower systems aren’t interchangeable with AR-15 uppers.

Do I need to check headspace?

Every Faxon barrel is headspace gauged with GO/NO-GO gauges when the extension goes on, and the BCG installed is the one this upper ships with. Checking headspace with GO/NO-GO gauges for the bolt you run is always good practice, and it’s a must any time you swap in a different bolt.

What bolt and magazines does a 350 Legend upper use?

Bolt: standard 5.56 / M16-pattern bolt (installed). Magazines: 350 Legend magazines.

What ammunition does it shoot?

350 Legend. Straight-wall 350 Legend loads, from 145 gr hunting loads up through heavy subsonics.

Can I run a suppressor on it?

Yes. The muzzle is threaded 1/2x28, so a direct-thread HUB adapter or a muzzle-device mount works. For a can that comes on and off, an adjustable gas block makes the rifle run softer suppressed.

What makes a good AR-15 upper, and how does this one compare?

Start with the barrel: steel, rifling, finish, and inspection. This one is 4150 CMV, button rifled, QPQ nitrided, borescoped, air gauged, headspace gauged, and 100% MPI inspected. Then a forged 7075-T6 receiver, a gas system matched to the barrel length (carbine-length here), a free-float M-LOK handguard, and, on a complete upper, a quality BCG. Faxon makes the barrel, receiver, gas block, and muzzle device, and assembles the upper in Ohio under a Lifetime Guarantee.

Nitride or chrome lining: which is better?

Chrome lining still has its place, mainly sustained automatic fire. For the vast majority of shooters, Faxon’s salt-bath QPQ nitride does what they need and more: it hardens the bore and exterior, resists corrosion, adds virtually nothing to the dimensions (a few ten-thousandths of an inch, about a tenth the width of a human hair), and needs little to no break-in.

Does the upper ship to an FFL?

No. The upper isn’t the serialized part of an AR-15, so it doesn’t require an FFL. Faxon lowers do. State and local laws on barrel length, threaded barrels, and muzzle devices still apply.

Where is it made, and what is the warranty?

Faxon makes the barrel, receiver, gas block, and MuzzLok® devices in Greater Cincinnati, Ohio, and assembles the upper there. It’s covered by the Faxon Lifetime Guarantee.

MuzzLok®, HARMONIX®, CORESYNC®, and Integral® are trademarks of Faxon Firearms. BREEK® is a trademark of its owner. Glock® and Colt® are trademarks of their owners; Faxon is not affiliated with them. “Plan B” is a trademark of Q, LLC; Faxon Firearms is not affiliated with, endorsed by, or sponsored by Q, LLC. Firearm, suppressor, and barrel-length laws vary by state and locality; know and follow the laws where you live.