It's likely the Spirit Gun Manufacturing Co. produces some of the best ARs you've never heard of. Headquartered in West Palm Beach, FL, Spirit Gun catalogs 22 models of carbines, rifles and pistols based on the AR design, but the company is a relative newcomer to the tactical market.
"We've been around for about four years, but we've mostly operated inside the trade," says Adam Trieschmann, Spirit Gun's director of operations. "We still have guys who call all the time and ask, 'Who are you?'"
Spirit Gun started out as an importer and supplier of high-end, traditional sporting firearms for a major retailer's fine-gun room. Later its focus shifted to the AR platform, with a continued emphasis on upper-level products. In fact, the company's ARs are manufactured, assembled and quality-checked under contract with aerospace and defense giant Abrams Airborne.
"These are not the creations of two guys in a back room putting together components," notes Trieschmann. "They are 100 percent made by a military-defense contractor to strict specifications and tolerances."
That's not to say Spirit Gun is confined to the conventional AR configuration. While the majority of its guns are stamped "5.56 NATO," several—like the new SGM-A41—are chambered for 6x45 mm cartridge. The SGM-A41 ups the performance ante without sacrificing reliability or needing specialized components to run.
Benchrest to Battle Zone
The 6x45 mm cartridge is simply the 5.56 NATO cartridge necked up to take a 6 mm, or .243-inch, bullet. The round got its beginnings in the mid-1960s, developed primarily for benchrest competition and varmint hunting. It proved to be capable of outstanding accuracy, helping Jim Stekl set an International Benchrest Shooters 200-yard Sporter aggregate record of .3069 MOA in 1973. Offering mild recoil and better resistance to wind drift than the 5.56 NATO due to its ability to accept heavier bullets, the 6x45 mm has also seen some use in the AR platform during NRA High Power competition.
Those heavier bullets allow rifles chambered for the 6x45 mm to send more energy downrange than their 5.56 NATO cousins. No doubt, the crowd that wishes traditionally chambered ARs came with more power will view that as a blessing. Black Hills recently began loading the 6x45 mm with three bullet choices: a 62-grain Barnes Varmint Grenade, an 85-grain Sierra GameKing and a 100-grain Sierra Spitzer.
The SGM-A41 I received for testing came with a 16-inch barrel. Five feet from the muzzle, the 62-grain load obtained 2,813 fps for 1,089 foot-pounds of energy. I chronographed the 85-grain load at 2,640 fps, which gave the GameKing 1,316 foot-pounds. The 100-grain load clocked 2,459 fps for 1,343 foot-pounds.
I found the external ballistics of the 62-grain 6x45 mm load were nearly identical to those of American Eagle's 5.56 NATO 62-grain full-metal-jacket load fired from a 16-inch-barreled carbine. Although on paper the 62-grain 6x45 mm may not appear to have an edge, the downright explosive nature of the Barnes Varmint Grenade will likely be more devastating on soft targets than a full-metal-jacket bullet at a similar velocity.
The 6x45 mm really comes into its own with the two heavier bullet weights. The closest 5.56 NATO factory load for which I had data to compare with the 85-grain 6x45 mm was the 77-grain Sierra MatchKing load from Black Hills—one of the heaviest factory 5.56 NATO loads available. It obtained 2,618 fps from a 16-inch barrel for 1,172 foot-pounds of energy, falling short of the 6x45 mm load by 144 foot-pounds. Hand-loaders can stuff 5.56 NATO cases with 80- and 90-grain bullets, but in a 16-inch barrel, there's little chance of these loads reaching the performance levels of the 85- and 100-grain 6x45 mm loads while staying within acceptable pressure limits.
According to Trieschmann, who worked with Black Hills and Les Baer Custom in developing the 6x45 mm loads, the factory ammunition operates at pressures of 48,000 to 51,000 CUP for reliable functioning in AR-style rifles without causing undue stress to internal components. In addition, the dimensional similarities the 6x45 mm shares with the 5.56 NATO—namely casehead diameter, case body diameter and overall cartridge length—make it an easy fit in the AR platform. As such, the 6x45 mm runs just fine with a standard bolt-carrier group and magazine. The only thing that needs to be swapped out, of course, is the barrel.
The SGM-A41 starts with Spirit Gun's proprietary lower, which features a unique backplate that's threaded to the rear of the receiver. Three holes cut into the backplate—one in line with the receiver and one on either side of it—accommodate a quick-detachable sling swivel. Shallow recesses milled into the rear of the lower correspond with the holes in the backplate to allow the base of the sling swivel to lock in place.
The SGM-A41 is replete with components from Vltor, which has been under the Abrams umbrella since 2004. The Vltor MUR-1A upper contains the BCM Gunfighter charging handle with an extended latch, along with a match-grade bolt-carrier assembly. While the MUR-1A adheres to mil-spec dimensions, it is built with thicker walls for increased rigidity and strength.
A fitting complement to the MUR-1A is Vltor's CASV-MT free-floating fore-end. The aluminum CASV-MT interfaces with the delta ring and includes an uninterrupted rail that, when the unit is installed, runs the length of the upper receiver and extends to the SGM-A41's mid-length gas block. The rear rail section clamps to the upper via two hex screws. Included with the CASV-MT are six rails in 2-, 4- and 6-inch lengths, which attach to the sides, top and bottom of the fore-end for mounting accessories.
The SGM-A41 I tested had a 16-inch Krieger stainless steel barrel with a low-profile gas block. The front sight was a Vltor CASV-M flip-up unit. Standard equipment includes a 16-inch Green Mountain chrome-lined, chrome-moly-vanadium barrel with an A2-style gas block, but you can special-order the gun with the components listed above. Same goes for the Geissele Automatics two-stage trigger in place of a single-stage mil-spec job. Rounding out the SGM-A41 is a TangoDown BG-16 BattleGrip, Vltor EMod buttstock and Midwest Industries SPLP flip-up rear sight.
Before I headed to the range, I topped the SGM-A41 with a Trijicon 5-20x50 mm AccuPoint in Warne rings. Since I didn't have to worry about the gap between the upper and the fore-end thanks to the CASV-MT's all-encompassing rail, I could mount the scope a bit forward where I like it.
At the 100-yard line, the SGM-A41 preferred the lightest bullet, but it still turned in a very respectable five-group average of slightly more than 1.25 inches with the 85-grain load. Trieschmann cautioned me that the barrel's 1:9-inch twist rate was a bit too slow for the 100-grain load, but I had to see for myself. He was right; groups widened to 4 inches with the heaviest bullet. If you plan to regularly shoot the 100-grain load, Trieschmann recommends a twist rate of 1:8.5 inches.
Tactical shooters looking for more power than the 5.56 NATO can find it in the 6x45 mm. Spirit Gun Manufacturing's SGM-A41 tempers the bigger-is-better approach with common sense, providing a carbine that offers benefits not only on paper, but also in the real world
Manufacturer: (561) 623-5980
Action Type: Gas-operated, semi-automatic
Caliber: 6x45 mm
Magazine Capacity: 30 rounds
Lower Receiver: Spirit Gun Manufacturing SGM-9; forged and machined 7075-T6 aluminum alloy
Upper Receiver: Vltor MUR-1A; forged and machined 7075-T6 aluminum alloy
Barrel: 16 inches; Krieger stainless steel with Vltor VC-A1 flash hider
Rifling: 6 grooves; 1:9-inch RH twist
Sights: Midwest Industries SPLP flip-up rear; Vltor flip-up front
Trigger: Geissele Automatics two-stage match; 2-pound, 6-ounce pull weight in first stage, 2-pound pull weight in second stage
Overall Length: 33 to 36.5 inches
Weight: 7.5 pounds
Accessories: One magazine, sling swivel, 6 fore-end rails, owner's manual