Brownells 350 Legend BRN-180 Hunting Rifle Build

posted on April 9, 2024
001 BRN350L Rifle Ready 01

Some folks outside of the shooting-sports community (and a few within) continue to wrestle with the idea of using AR-15 rifles for hunting. I believe this is due in part to a lack of information regarding the AR platform, or Modern Sporting Rifle if you prefer, and its modularity. Many ARs are chambered in .223 Rem./5.56 and configured for target shooting, varminting or home defense. But this same gun can be quickly converted into a medium- or large-game hunting rifle by swapping out the upper for one chambered in calibers such as 6.5 Grendel, .300 BLK, 7.62x39 mm, 350 Legend or .450 Bushmaster.

For those who are not interested in owning a collection of firearms, one AR lower with a pair of uppers in different calibers can cover most—if not all—of an individual's rifle needs. Recently Brownells expanded its series of factory complete BRN-180 upper receiver assemblies to include a 16-inch barrel model chambered in 350 Legend. I've worked with these piston-driven uppers chambered in .223 Wylde in the past and found them to be reliable and enjoyable to work with. I’ve also found good reasons to be enthusiastic about the flexible and more comfortable shooting 350 Legend cartridge. 

BRN 180 Upper

The launch of this new upper presented an ideal opportunity to team up with the good folks at Brownells to pull together a batch of components and tools to assemble a flexible, do-most BRN-180 package. The company makes finding what you need for an at-home build easy because almost all of the components and tools shown here were available through the Brownells' online catalog at the time this build was conducted. The one exception was the new-for-2024 pistol grip which was not in stock just yet. Here's a closer look at how the factory assembled Gen 2 BRN-180 350 Legend upper and an at-home lower build came together and performed at the range. 

The Gen2 BRN-180 350 Legend Upper

Inspired by Eugene Stoner's AR-18/180 design, the BRN-180 series of uppers were developed by Brownells in conjunction with Primary Weapon Systems and Foxtrot Mike Products. Like other members of this series, this version of the Gen 2 BRN-180 upper employs a short-stroke gas-piston system to cycle the action. The flat-top upper receiver is milled from a billet of 7075-T6 aluminum and treated with a hardcoat anodized finish. A spring-loaded polymer dust cover graces the ejection port. This design does not incorporate a forward assist button but it is compatible with standard, Mil-Spec AR-15 lower receivers.

BRN 350 Legend Upper

Inside the receiver is a block-shaped bolt carrier group with a rotating multi-lug bolt. Fitted with a right-side reciprocating charging handle, this carrier slides back and forth along a pair of guide rods set into the polymer end cap. The two recoil springs (one per rod) generate more pressure than those used in the .223 Wylde uppers. I found out for myself that it's enough of an increase that they will launch the entire recoil assembly out of the upper if not manually held in place when separating the receivers.

BRN 350 Legend upper

This upper is outfitted with features designed with 350 Legend hunting loads in mind. In particular, the feed ramp has been resized to accommodate a variety of bullet types and the wider 350 Legend cartridge case. The 16-inch barrel features a lightweight contour, a 1-16” rifling twist rate and a muzzle threaded at 1/2x28 TPI to accommodate a variety of muzzle devices sized for .357-caliber or larger bullets. A knurled thread protector is provided. 

BRN 350 Legend Upper Gas Port

Some versions of the BRN-180 upper require the gas pistons to be swapped out in order to use a sound suppressor. This model sports a much more convenient, exposed two-position adjustable gas block. Two access points are located along the top of the 13-inch machined 7075-T6 aluminum handguard. One is a small port to view the gas-block setting: “1” is for unsuppressed shooting, while “2” is for use with a suppressor. The setting is switched through a 0.5-inch gap in the handguard rail using the provided wrench or a similar pin-punch like tool. The handguard’s vents along the right, left and bottom edges also serve as M-LOK accessory attachment points.   

BRN350 Upper Muzzle

Assembling the BRN-180M Lower Receiver

Brownells offers the in-house BRN-180M stripped lower receiver which is milled from a billet of 7075-T6 aluminum and treated with a hardcoat-anodized finish. Taking advantage of the upper's internalized recoil system, a milled-in vertical four-slot 1913 Picatinny rail takes the place of the buffer tube port. This short rail can support a variety of clamp-on folding stocks (more on those later). Other features include a threaded bolt-catch pin, flared magazine well, oversized integral trigger guard and a captive set screw for the takedown pin detent spring.

BRN 180 Add on parts

The small parts and controls were taken from a CMMG Lower Parts Kit. This particular kit (SKU: 55CA6B8) included an ambidextrous selector. I've worked with a variety of CMMG kits over the years with positive results. However, the Mil-Spec trigger group and A2 polymer grip were both replaced with upgrades from other manufacturers.

Since this is intended to be a multi-purpose lower used with multiple uppers, I went with a trigger I knew I would enjoy. The CMC Triggers' Black drop-in, single-stage trigger group is a Brownells exclusive (SKU: 207000135). It features an aluminum housing, a flat-faced competition style trigger and a lightened hammer powered by a Rocket Wire spring. It's listed as having a fixed 3-pound 8-ounce trigger pull weight. But my Wheeler digital trigger gauge insisted, repeatedly, that this trigger has a short, crisp trigger stroke which breaks cleanly with an average of 2-pounds 14-ounces of trigger pull. 

BRN 350 Legend parts

For this build, the lower was outfitted with an adjustable Engage polymer grip from Mission First Tactical. This company has taken a page from the polymer-framed pistol grip design book by including three interchangeable backstraps. The Engage also includes three interchangeable front straps along with a rubber grip plug and battery plate which turn the grip's hollow center into a handy storage compartment. These straps were traded in and out until I found a shape that was just right for me. The panels were then secured in place using the provided polymer pins.

BRN 180 350 Legend Lower Receiver

With the upper arriving ready to use and no buffer assembly to install, populating the lower is a fairly simple process by AR-building standards. It was time to replace some of my more bedraggled pin punches and upgrade other tools, so I requested two Real Avid tool kits that came in handy for this trip around the bench.

AR Tools and punches

For assembling the optic mount, the SMART-TORQ driver set made it easy to tighten the mounting screws to just-right tightness thanks to the adjustable inch-pound increment settings of the handle. This system provides visual, tactile and audible indicators to avoid over tightening and it arrives with a set of a dozen of the most common bits in the zippered storage case. The Master Bench Block Pro Kit is a compact, general-purpose gunsmithing tool set which includes a complete range of standard and roll pin punches, a hammer with interchangeable heads, a pin alignment tool and a rubber over-molded Smart Block to use as a work surface. In addition to the handy magnetized pocket for small parts, the polymer trays lock together into a handy storage box.

Folding Stocks

As with any adjustable shoulder stock system, left-side folders have their trade-offs. In this case, the four stocks shown here sacrifice the six-position adjustable length-of-pull (LOP) common to buffer-tube AR-15 platforms in favor of a relatively simple, rugged and lightweight construction. It was quite interesting to see how each stock affected the rifle's cosmetics and handling.

BRN-180 350 Legend

First up was the Brownells BRN-180 1913 Picatinny Mount stock which features an aluminum two-bolt hinge, a black polymer body and a fixed rubber buttpad. Weighing in at 14.6-ounces, it was the lightest of the stocks with a 13.25-inch LOP. This stock was the best fit for me and an ideal multi-purpose option. However, it also cost the most and it was necessary to really lean into the fairly stiff hinge when extending or folding the stock.

BRN 180 350 Legend with stock folded

Midwest Industries, Inc., offers a variety of top-notch folding stocks with heavy-duty folding mechanisms constructed from heat-treated 4140 steel that proved to be easy to work with. The aluminum Extruded Stock (SKU: MI-STAP-SF-FES) borrows its profile from AK-47 stocks. The skeletonized body has a curved and grooved butt plate, provides a 13-inch LOP, sports a total of five QD sling ports and weighs sixteen ounces. It looks great and provides a better cheek weld than one might expect.

BRN 180 350 Legend with skeletonized stock

The Midwest Industries aluminum Lightweight Stock (SKU: MI-STAP-SF-LWS) is about as minimalist as one can get. The vented straight bar has a nicely rounded top surface for a positive cheek weld and it sports three QD sling ports. It’s capped off with a solid aluminum, wedge-shaped textured end plate secured in place by a pair of screws. Although I like this stock for some purpose-built applications, with its relatively short 12.5-inch LOP I think it's the least likely of the bunch to find its way on to a hunting gun.

BRN180  with six position stock

The last of the pack was the stock used for the range test. It's the Midwest Industries polymer-bodied Trapdoor model. With a profile very similar to that of the Brownells stock, it weighs 18.7-ounces, has a 14-inch LOP and a raised-ridge textured polymer buttplate. Using the tip of a .223 Rem. cartridge, or similar tool, pressing through a small port in the top of the stock releases the hinged trapdoor buttplate so that it swings open to provide access to the storage compartment inside. It's a handy space for hunters to keep gun maintenance or survival supplies. The compartment is not water resistant but the judicious use of a self-sealing plastic bag will do the trick.

BRN180 with fixed stock

Magazines & Optic

When it came time to select magazines for this review I went straight for CMMG's straight-bodied aluminum 350 Legend AR-15 magazines. I've worked with them before and found them to be utterly reliable with this caliber. This company offers five- and 10-round options ($19.95), both of which have the same external dimensions, which only protrudes about half an inch out of the magazine well. CMMG is one of the few companies to offer 20-round magazines in this caliber ($24.95). Although these boxes hold too many rounds for use in the field in many regions, they are quite handy for use on the range or for home defense.

BRN 180 magazines

Generally speaking, folks in the know agree that the 350 Legend straight-walled cartridge is effective to a range of around 200-yards. Some say it can be ethically stretched out to 250-yards while others choose to keep their shots to a maximum distance of about 150-yards. Within these relatively short shooting distances there's plenty of room to use a variety of optic types, depending on the skills and preferences of the hunter.


With this in mind, informal and formal range testing was conducted using a Swamp Fox Arrowhead LPVO 1-8x24mm SFP III. This model features a second focal plane (SFP), glass-etched Guerrilla Dot BDC reticle with 12 brightness settings for the CR2032 button cell battery powered green illumination. Other features include a 30mm tube, 0.5-MOA click adjustments and push/pull locking turrets with a zero reset. This optic was secured to the rifle using a lightweight 7075 aluminum Swamp Fox Freedom cantilever mount. Whether or not folding back-up sights belong on a hunting rifle is something the owner will have to decide for themselves. But for those who do like a set of irons, just in case, some of the photos of the BRN-180 350 Legend upper can be seen outfitted with a set of Brownells HK-style folding battle sights (SKU: 760-001-901, $195.99).

At The Range

The various elements of this BRN-180 build came together to form a rifle that was enjoyable to shoot at the range. The felt recoil generated by 350 Legend ammunition fired from carbine-sized long guns is more pronounced than .223 Rem. Nevertheless, it's a moderate level of kick in the .30-30 Win. range that most shooters should find all-day comfortable to work with.

BRN 180 in lead sled

Brownells takes pains to point out that this upper's feed ramp is among the most reliable available, and for the most part it was. The first 10-rounds through the gun were Hornady American Whitetail 170-grain soft point. The very first round into the chamber went click instead of bang with what could have possibly been a soft primer strike. But no other failures to fire occurred in the course of testing. This same load also produced a couple of failures to feed early on with the soft points mashed up against the feeding ramp as the bolt assembly cycled.

But after the first CMMG magazine was emptied through the gun the malfunctions cleared up. There were no failures after that even when using the same ammunition or when the first magazine was reloaded and fired again. My best guess is that the components needed a few rounds fired to settle in and get to work. Formal 100-yard, bench rested three-shot group accuracy testing included the Hornady Whitetail rounds along with Underwood Ammo TSX and Winchester Deer Season XP loads. Here are the results including 10-round bullet velocities measured using a Garmin Xero C1 Pro chronograph:

BRN 180 350 Legend Ballistic results

Parting Shots

The answer to the question of why someone would choose to hunt with an AR-15 is simple. The features which make the AR a popular option for use by law enforcement personnel and civilian self defenders are the same features hunters are looking for. These carbines are handy, relatively light weight, comfortable to use, a good fit for a variety of body sizes and skill levels, and these guns are much easier to customize than many bolt-action or lever-action rifles. Add in the variety of quick-change caliber options currently available and what’s not to like?

With Brownells' BRN-180 uppers previously available chambered in .223 Rem., .300 BLK and 7.62x39 mm, the 350 Legend is a welcome addition. The robust BRN-180 piston system paired with this rifle's AR-15 modularity makes for a handy, flexible and reliable carbine. And the Brownell's one-stop shopping catalog makes it easy to get the features you want.

BRN 180 350 Legend Lower receiver stamp

Components & Tools:

  • .223 Wylde Upper (Shown): Brownells BRN-180, 16" barrel (#078000600) $849.99
  • 350 Legend Upper (Tested): Brownells BRN-180, 16" barrel (#430103461) $899.99
  • Stripped Lower Receiver: Brownells BRN-180M (#080001382) $159.99
  • Lower Parts Kit: CMMG with ambidextrous selector (55CA6B8) $74.95
  • Trigger Group: Brownells exclusive CMC Black Single-Stage, flat-faced trigger (#207000135) $174
  • Pistol Grip: Mission First Tactical Engage EPGI16-BL, $34.99 (from Manufacturer)
  • Shoulder Stock (Shown): Brownells BRN-180 Folding Stock, Polymer (BRN-180-BP), $209.99 
  • Shoulder Stock (Shown): Midwest Industries Extruded Aluminum (MI-STAP-SF-FES) $165.99
  • Shoulder Stock (Shown): Midwest Industries Light Weight Aluminum (MI-STAP-SF-LWS) $152.99
  • Shoulder Stock (Tested): Midwest Industries Trapdoor, Polymer (MI-STAP-SF-TRAPDOOR) $189.95
  • Optic: Swampfox Optics Arrowhead LPVO 1-8x24mm SFP III Guerrilla Dot BDC, Green, $415
  • Scope Mount: Swampfox Optics 30 mm Freedom Light Cantilever, Black, $105
  • Magazines: CMMG 350 Legend Straight Profile Aluminum, $19.95 - $24.95 
  • Optics Driver: Real Avid Smart-Torq Precision Driver (AVSTORQ) $79.99 
  • Bench Block: Real Avid Master Bench Block Pro Kit (AVMBBPKIT) $79.99


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