FAXON DUTY SERIES GUNNER PROFILE 16" CARBINE-LENGTH .450 BUSHMASTER AR15 BARREL

Rifle Barrels › Duty Series › .458 SOCOM / .450 Bushmaster › 16″ Gunner, Carbine-Length  |  Works with: .450 Bushmaster BCG • .875″ gas block • carbine-length gas tube • 11/16x24 muzzle devices

Why a 16″ .450 Bushmaster, and Why the Gunner Profile

.450 Bushmaster was designed to put a big-bore hunting cartridge in a standard AR-15: a .452″ bullet from a straight case that fits a 5.56-pattern magazine body, runs on a standard upper and lower, and needs only a bolt with a .308-size face. In the states that require a straight-wall rifle cartridge for deer it is the round that hits hardest, and it is the choice over 350 Legend when the game is bigger than whitetail, when the shot is through brush, or when you want a hog and bear rifle with the same muscle memory as your 5.56. From a 16″ barrel a 250 gr load leaves at about 2,200 fps and a 300 gr at about 1,900, with enough left to expand and kill cleanly to 200 yards, which is where Faxon and the ammunition makers draw the line. Sixteen inches is the length Faxon recommends for the cartridge: the powder is burned well before the muzzle, so a longer barrel adds almost nothing, and a 16″ carries through the woods. Faxon’s 350 Legend vs 450 Bushmaster comparison covers which straight-wall cartridge is the right one for your hunt.

A .45-caliber bore takes most of the steel out of a 1″ blank, so this Gunner is built heavier than the 350 Legend and 300 Blackout versions: a .980″ chamber journal, a straight .875″ body behind the gas block instead of a Government taper, an .875″ gas journal, and a taper from .750″ to .725″ ahead of it. The body is where the barrel gets its stiffness and where the wall around the chamber and port has to be; the taper is where a barrel gets heavy without getting stiffer. At 16″ the result is 1.72 lb, about six ounces over the 350 Legend Gunner and still lighter than most heavy-profile 5.56 barrels, in a rifle that recoils like a 20-gauge. A carbine-length gas system with a .116″ port runs the low-pressure cartridge with a standard buffer, and the 11/16x24 muzzle takes Faxon’s MuzzLok .450/.458 brake, which is worth having on a 250 gr load. If you hunt where 350 Legend is enough, the 16″ 350 Legend Gunner is six ounces lighter and runs a 5.56 bolt; the 16″ .458 SOCOM Gunner is the same big-bore recipe for a bottleneck case where straight-wall rules do not apply.

What “Duty Series” Means

Duty Series is Faxon’s 4150 CMV line: the M4/M16 barrel alloy, salt-bath QPQ nitrided inside and out. 4150 carries about 0.50% carbon plus vanadium, which gives it more strength and wear resistance at temperature than 4140, and nitride adds a hard, corrosion-resistant surface to the bore and exterior without plating anything, and it adds virtually nothing to the surface: a few ten-thousandths of an inch, roughly a tenth the width of a human hair. It is the right combination for a barrel that will be shot hard, carried in the weather, and cleaned when there is time. Faxon’s stainless Match Series is the option when you want the precision-barrel formula; the Duty Series is the one to reach for when the rifle has a job.

What’s in the Box

How It’s Made

Every Duty Series barrel is made start to finish in Faxon’s Greater Cincinnati plant, on Faxon’s machines, to Faxon’s prints. This is the routing for this barrel.

1. Drill and pull-ream 4150 CMV bar is gun-drilled, then pull-reamed from the chamber end to a .443″ bore held to ±.001″, with a 32 Ra maximum finish checked on a profilometer and a borescope pass for reamer marks.
2. Button rifle A carbide button is pulled through from the chamber end to form six grooves, right-hand, one turn in 16 inches, to a .450″ groove diameter. Bore and groove are air-gauged.
3. Stress relieve and qualify The rifled blank is stress relieved before it becomes a finished barrel, then the OD is qualified true to the bore so every later cut references the same axis.
4. Turn the Gunner profile Muzzle end first: the .875″ gas journal is turned to .8740–.8750″ and checked with a micrometer on every barrel, held within .005″ of the bore, the Gunner taper ahead of it is turned true to the same axis, and the 11/16x24 muzzle is threaded and crowned with a ring cut into the shoulder to mark it .450 Bushmaster. Then the breech end: the .875″ body, the .980″ chamber journal, and the extension thread.
5. Chamber The .450 Bushmaster chamber is cut and checked with a headspace gauge; chamber surfaces are held to a 20 Ra finish.
6. MPI and nitride The machined barrel is 100% wet magnetic-particle inspected for surface and near-surface flaws, then salt-bath QPQ nitrided inside the bore and out, hardening the surface while adding virtually nothing to it.
7. Gas port, extension, pin After nitride, the .116″ gas port is drilled and reamed through the .875″ journal, the Big Bore M4 extension is torqued to 150 ft-lb and pinned, and the barrel is headspaced with a .450 Bushmaster go/no-go gauge.
8. Mark The Faxon shield and order number are laser-engraved on the chamber journal and “.450 BUSHMASTER 1-16T” ahead of the gas block.

What Reviewers and Owners Say

Voted Favorite Aftermarket Barrel by Shooting Sports Retailer every year since 2022 — the Gold Award, the top honor in the category. Faxon also took the Tactical Retailer Gold Award in the same category in 2025. Here is what independent testers and buyers have said about Faxon barrels and this one.

5.0 stars on FaxonFirearms.com. This barrel is also carried at OpticsPlanet and MidwayUSA; the 350 Legend Gunner it shares its Big Bore recipe with is rated 5.0 at Primary Arms.

Build It Out: Faxon Parts That Fit This Barrel

Everything below is made or specified to the same prints this barrel is, so the gas system, extension, and muzzle line up the first time. Pick one from each row and the upper is done.

Duty Series 16″ Gunner .450 Bushmaster FAQs

Is this a SAAMI .450 Bushmaster chamber, and what bolt and magazines does it need?

Yes, a SAAMI .450 Bushmaster chamber, headspaced with a .450 Bushmaster go/no-go gauge after the extension is installed. The cartridge fits a standard AR-15 upper and lower, but its .473″ rim is the same as a .308’s, so it needs a bolt cut for it: Faxon’s .458 SOCOM / .450 Bushmaster bolt and bolt carrier group have the .125″ bolt-face depth the cartridge calls for, and a 5.56 bolt will not work. It also needs .450 Bushmaster magazines, which are 5.56-pattern bodies with a single-stack follower, because the fat case will not feed from a standard 5.56 magazine. This barrel’s Big Bore extension has its feed ramps opened up for the .500″ case and it ships headspaced. The upper receiver has to match it: Faxon requires its Enhanced Forged Big Bore upper for every .450 Bushmaster and .458 SOCOM barrel, because its feed ramps and ejection port are opened up for the bigger case and a standard 5.56 upper will not feed and eject it reliably. So the build is barrel, Big Bore upper, bolt, and magazines.

Why carbine-length gas on a 16″ .450 Bushmaster, and what does it need to run?

Because .450 Bushmaster is a low-pressure, fast-burning straight-wall cartridge that needs its port early to catch enough gas: carbine-length puts it about 7.7″ from the breech with eight and a half inches of barrel past it, and Faxon reams it to .116″, a third larger than a 5.56 port, to make up for the lower pressure there. With factory 250 to 300 gr ammunition it cycles with a standard carbine buffer and spring and a .450 Bushmaster bolt carrier group. A .45-caliber bore moves a lot of gas, so if a suppressor or a brake is in the plan, an adjustable block lets you bring it back down. This barrel needs a carbine-length gas tube.

What is the Gunner profile, and why is the .450 Bushmaster version built with a straight body?

Faxon’s hybrid contour: full diameter where the barrel gets its stiffness (the chamber journal and the body behind the gas block) and tapered ahead of the block where mass only adds weight. Because a .452″ bore leaves very little wall in a 1″ blank, the .450 Bushmaster Gunner runs a straight .875″ body and an .875″ gas journal where the 5.56 Gunner runs a Government taper and a .625″ journal, and it tapers to .725″ ahead of the block instead of .500″. That is why it weighs 1.72 lb at 16″, and why it takes the .875″ low-profile block instead of the .750″.

Why 1:16 twist, and what bullets does it stabilize?

Because .450 Bushmaster shoots short, heavy .452″ bullets at moderate velocity, and a short bullet needs very little spin to fly straight. Faxon rifles it 1:16, faster than the 1:24 the cartridge was specified with, which gives the 250 and 260 gr hunting loads more margin and stabilizes the 300 gr loads and heavy subsonics that a 1:24 can leave marginal. From a 16″ barrel the 250 gr loads leave at about 2,200 fps with roughly 2,700 ft-lb, which is why the cartridge is a 200-yard deer and hog round that hits like a .45-70.

What gas block and gas tube does it take?

A .875″ gas block on the 1.9″ journal and a carbine-length gas tube. Faxon makes a .875″ adjustable and a .875″ fixed low-profile block, and a 304 stainless carbine-length gas tube. The gas port is reamed to .116″.

What does 4150 CMV mean?

Chrome-moly-vanadium steel with about 0.50% carbon, the alloy the M4 and M16 barrel specification calls for. The higher carbon and the vanadium give it more strength and wear resistance at temperature than 4140, which matters most on a barrel that will see fast strings and sustained fire.

Is the nitride inside the bore?

Yes. Salt-bath QPQ nitride is a diffusion treatment, not a plating, so it hardens the surface of the bore and the exterior while adding virtually nothing to it: the surface grows by a few ten-thousandths of an inch, .0002–.0004″, roughly a tenth the width of a human hair or about the diameter of a single red blood cell. It also gives the barrel its corrosion resistance and matte black finish.

Does it come with a gas block, gas tube, or muzzle device?

No. It ships with the black-oxide Big Bore M4 extension installed, torqued, pinned, and headspaced. Gas block, gas tube, and muzzle device are sold separately; the muzzle is threaded 11/16x24.

Will it work with a suppressor?

Yes. The 11/16x24 muzzle takes a .45-cal or .458-rated can on an 11/16x24 mount, never a .30-cal or .36-cal can, and a carbine-gas 16″ big-bore straight-wall cartridge over-gasses with a can more than a 5.56 does, so the adjustable block is part of the setup. For a rifle that runs suppressed most of the time, pair it with the Faxon .875″ adjustable gas block so you can bring the gas down.

Is .450 Bushmaster legal for deer in straight-wall states, and how far will it hunt?

It is the cartridge those rules were written around. Ohio, Michigan’s southern zone, Iowa, Indiana, and other states with straight-wall rules allow .450 Bushmaster for deer, and its 1.70″ case sits inside every case-length limit on the books, though every state writes its own rules, so check the current regulations where you hunt. From a 16″ barrel a 250 gr hunting bullet leaves at about 2,200 fps and carries enough velocity to expand and enough energy for deer, hogs, and black bear to about 200 yards, which is where Faxon and the ammunition makers put the practical limit. Inside that range it hits harder than a .45-70 factory load, with recoil closer to a 20-gauge slug than a 12.

How fast does .450 Bushmaster leave a 16″ barrel?

About 2,200 fps with 250 gr loads, 2,150 with 260 gr, and 1,900 with 300 gr, depending on the load, or roughly 2,700 ft-lb at the muzzle. The cartridge burns its powder early, so a longer barrel adds very little; 16″ is the length Faxon recommends as the best balance of velocity, accuracy, and handling for it.

.450 Bushmaster or 350 Legend?

350 Legend if the hunt is whitetail inside 200 yards and you want the lightest rifle, the least recoil, and a barrel that runs a 5.56 bolt. .450 Bushmaster if the game is bigger, the cover is thicker, or you want the hardest-hitting straight-wall round an AR-15 can fire: about 50% more muzzle energy and a .452″ bullet that opens a bigger wound channel, at the cost of six ounces of barrel, a dedicated bolt, and recoil you will notice. Faxon’s comparison article walks through the choice load by load.

Is the gas journal dimpled for set screws?

No. The journal ships round so any .875″ low-profile, clamp-on, or pinned gas block fits the 1.9″ journal. A set-screw block holds on the nitrided journal when its screws are torqued with thread locker; if you want dimples, mark them through the block’s screw holes and drill.

Where is it made, and what is the warranty?

Made in Greater Cincinnati, Ohio, from bar stock to finished barrel, and covered by the Faxon Lifetime Guarantee.

Dimensions are from the Faxon engineering print and inspection sheets for this SKU; weight is nominal. Gas block, gas tube, and muzzle device sold separately. Owner reviews are quoted as written from FaxonFirearms.com product reviews; press quotes link to their sources. Award: Shooting Sports Retailer Choice Awards, Favorite Aftermarket Barrel, Gold. Covered by the Faxon Lifetime Guarantee.