At 4 pounds, 13 ounces, the SP-ARC is a breeze to carry.
September 25, 2024
The idea for this AR occurred on a spring bear hunt in the steep mountains of Idaho. During a thigh-straining ascent, my buddy and I stopped for a breather. Leaning his heavy bolt-action against a tree, he asked the average shot distance of our bear kills in the area. I thought back on past hunts and crunched the numbers.
“All our kills have been inside 300 yards,” I said. “Hard to believe, huh?”
“You’re kidding?” he said. “In other words, I’m packing a 500-yard rifle on a 300-yard hunt.”
He had a point. Of the eight bears we’d taken, the average distance was 280 yards. Using that data, I began scheming a minimalist backcountry rifle build that was easy to carry, lightweight, and compact, yet possessed the accuracy and energy to cleanly kill a bear inside 300 yards. The resulting firearm is seen here, a bolt-action AR I call the Special Purpose ARC (SP-ARC).
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CARTRIDGE: 6MM ARC
The ARC in SP-ARC stands for Hornady’s 6mm Advanced Rifle Cartridge (ARC). This mild-mannered round slings 108-grain Hornady ELD-M bullets at 2,500 fps from a 16-inch barrel. At an elevation of 4,000 feet, the bullet carries 1,000 ft-lbs of energy to 325 yards, a distance where the sleek projectiles drift only 7.8 inches in a 10-mph crosswind. The ARC is no powerhouse, but it’s ideal for this. Cartridge selected, I began the hunt for a special barrel — one that was lightweight and accurate yet lacked a gas port. Unlike standard ARs, the SP-ARC is a straight-pull repeater.
UPPER: MINIMALISM
My first call was to Aaron Painter, the founder and owner of BSF Barrels. After explaining what I was after, Painter said, “No problem. We can do that.” A few months later, a beautiful BSF Barrel arrived, configured exactly as I’d specified. BSF’s barrels are unique. Unlike carbon-fiber wrapped barrels, BSF tensions a carbon-fiber tube over a lightweight steel barrel. It’s an ingenious design and accurate, too. Carbon-fiber barrels are never cheap, but BSF is the best value around. To connect barrel and upper, I used a carbon-fiber handguard designed for blowback-operated pistol-caliber carbines. It’s too narrow to work with a gas block and gas tube, but since the SP-ARC has no gas system, that’s no problem. The upper receiver, however, did require custom work beyond my plug-and-play capabilities. Fortunately, gunsmith and contributor Ned Christiansen came to my rescue. Christiansen chopped a standard AR bolt carrier behind the firing pin and drilled and tapped the carrier’s right side to accept a Grade 5 titanium Custom Charge Handle from Nottingham Tactical. To provide clearance behind the ejection port, he milled a slot for the knob to reciprocate. The results are functional and simple. Thanks again, Ned!
LOWER: POLYMER GALORE
The lower is from Kaiser US Shooting Products. These are sold as a matched upper/lower pair. Constructed of reinforced polymer, the X-7 lower receiver is lightweight, durable, and handsome. Inside the trigger pocket rests a TriggerTech Adaptive unit, which is probably the finest component of the build. It’s not, however, the most radical. That honor goes to AGP Arms’ folding stock. Built for rimfire ARs that house all the moving parts in the receiver (i.e., no buffer tube), the AGP Arms stock is a cool design that pairs nicely with the straight-pull SP-ARC. Weight wise, it’s not the lightest stock option, yet the ingenious folding mechanism makes up for this. Folded, the SP-ARC measures a hair over 24.5 inches, which is shorter than the barrel alone on many long-range hunting rifles. Strapped on the side of a pack, the SP-ARC is hardly noticeable, and unlike other rifles, the barrel won’t catch on overhead branches. Rifle complete, it was time to mount an optic. Again, I stuck to simple and functional.
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OPTIC & MOUNT: AERO PRECISION & WEAVER
For lightweight AR mounts, there’s one choice: Aero Precision’s Ultralight mount. This is a solid option for any AR, but for lightweight builds, it’s all I use. It’s streamlined, simple, and affordable. Next up was a scope. Inside 300 yards, a high magnification optic with an adjustable elevation turret is just dead weight, so I chose a Weaver Classic 4x28mm. This discontinued optic is sleek and compact, and while it’s built for rimfires, the Japanese-made scope holds up fine to centerfire recoil. It weighs just 8.5 ounces, and for the SP-ARC’s max range of 300 yards, 4X is plenty magnification. Once installed and boresighted, it was time to hit the range.
RANGE TIME: HOW’S IT WORK?
During function testing, I noticed two things. 1) The plastic stock on this lightweight rifle transmits more recoil than expected. It’s not painful, but in a 4-pound, 13-ounce package, you feel it. 2) Cycling the carrier after firing a round requires effort. This isn’t smooth like a traditional bolt-gun. Using a LabRadar chrono during rough zeroing, I fired 10 rounds of Hornady’s Match 108-grain ELD-M. The average velocity was 2,498 fps. To maximize trajectory, I used a 300-yard zero, a technique I learned from Kifaru founder Patrick Smith. As seen in the ballistic chart, this is a radical zero that results in a bullet striking high — up to 6.1 inches at 150 yards — inside 300 yards. To prevent misses, Smith uses a brisket (belly line) hold for common distances. As distance increases, he begins holding higher. According to Smith, this method is faster and easier than judging drop. On paper, it seemed like the way to go. I finetuned windage and elevation at 100, 200, and 300 yards on steel plates. At 200 yards, a palm-sized clump impacted almost 6-inches high. At 300 yards, 5 rounds impacted dead-on in a circle the size of a softball. Excellent. Time to go further. At 400 yards, groups opened up, but that’s to be expected when shooting a lightweight rifle off a pack. Simulating a wounded animal, I held approximately 13-inches high and carefully sent 3 rounds. Each round impacted steel.
FINAL VERDICT: USEFUL OR USELESS?
Is a straight-pull, ultralight AR for you? Not likely. Countless hunting rifles will outperform this gun. However, for weirdos like me who climb vertical ridges in the wilderness for one crack at a bear, this minimalist tool has merit. The SP-ARC is lightweight, accurate, folds, and carries ample energy to 300 yards. Even though it’s purpose-built for a specific animal in a specific area, since completing the build, I’ve found another use for it. In Wyoming, I cover vast tracts of ground with shotgun in hand during upland season. By stuffing the SP-ARC and a predator call in my pack, I can score a bonus hunt when a spot looks promising. Not bad, huh? I’m not sure what the total cost of this build is, but I’d guess around $1,500, which is dirt cheap for a custom, one-off rifle. This project yet again reminded me why the AR-15 is the greatest firearm design ever made. Like Burger King, you can “Have it your way.”
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