AllTerra Arms Mountain Shadow Carbon Bolt-Action Centerfire Rifle

A lot of firms out there are building custom bolt-action rifles for big game hunting. There is seemingly no end to high-end production, semi-custom and custom rifles on the market. Prices and quality run the gamut. In 2015, Andrew Foster set out to be different from the rest. He founded AllTerra Arms in Boise, Idaho, with the hope of “designing, patenting, and building the most accurate and reliable rifle on the planet.”

AllTerra’s Mountain Shadow Carbon is one of the rifle designs that evolved from Foster’s vision. Customers can choose from off-the-shelf rifles or use AllTerra’s website to custom-configure their own creations. Choices begin with choosing the basic rifle model, a right- or left-handed action and chambering. The stock is next, and buyers can customize length-of-pull, various camo patterns and even choose the style of sling swivel stud or hardware desired.

Barrel length is the next choice, followed by several trigger and floorplate options. Eight different metal finishes are available, all of them Cerakote. The final choice is which mount and optic are desired, with options from Leupold, Nightforce, Steiner, Swarovski, Kahles and Zeiss. AllTerra will mount a customer-provided scope for a fee.

AllTerra’s Mountain Shadow Carbon is built on the company’s precision-made Convergence action. The action is CNC machined on pre-hardened 416 stainless steel. This is tough on tooling and is more expensive to produce, but it eliminates the possibility of warpage during the heat-treat process.

The bolt raceways are EDM cut, another expensive and time-consuming process that produces excellent results. The Convergence has an integral recoil lug, a side-mounted bolt stop and a TriggerTech Primary trigger. This trigger is user-adjustable, and my sample broke cleanly at 2.1 pounds right out of the box.

The action uses a dual opposing lug bolt setup, similar to that of the Remington 700 and its clones. The bolt is machined from hardened 4140 chrome-moly steel. The bolt handle is machined from the same billet as the bolt body, eliminating a potential failure point. The bolt handle is skeletonized.

A mini M16-type extractor is used along with two plunger-style ejectors. In addition, the ejection port is machined oversize to allow plenty of room for loading or unloading the chamber. Unlike some rifles out there, the Mountain Carbon Hunter cleanly ejected loaded rounds, something that is sometimes necessary in the real world. The entire feeding, ejection and extraction system proved to be very reliable during my testing.

Although detachable magazines are available as an option, the standard Mountain Shadow Carbon uses an internal magazine with a hinged floorplate. I prefer an internal magazine over the detachable variety on a hunting rifle because it’s one less thing to lose in the field.

The steel magazine box is extended in length to allow for the long VLD-style bullets that are becoming so popular thanks to their ballistic properties. The bottom metal is fully machined from aluminum as is the magazine’s follower. The floorplate can be released using the button inside the trigger bow, dumping the magazine all at once. In 6.5 PRC, the magazine has a 3+1 capacity, which is pretty standard for that chambering.

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As the name suggests, the 20-inch barrel on the Mountain Shadow Carbon is carbon-fiber-wrapped. The contour is similar to the Proof Sendero Light that I’ve used on several rifle builds. I am a fan of the shooting and handling characteristics of this contour. The barrel is threaded 5/8x24 at the muzzle. The test rifle included an eight-port muzzle brake that all but eliminated the felt recoil of the 6.5 PRC.

The stock on the Mountain Shadow Carbon is a proprietary design that is available in various colors and camouflage patterns. The stock has a semi Monte Carlo-style cheekpiece and some reverse drop on the comb. The pistol grip is a comfortable compromise between that of a traditional sporter and many of today’s nearly vertical designs.

The fore-end swells outward to a semi-beavertail profile that is conducive to shooting from rested positions. Both the fore-end and pistol-grip sections are textured to make things less slippery when wet. On my test rifle there is a traditional sling swivel stud at the toe of the stock and a Picatinny rail section where the forward stud would usually be found. This not only allows for the easy mounting of a bipod or tripod, but also offers a QD-style female sling swivel attachment point.

The barreled action is pillar-bedded inside the stock, and the barrel is free-floated the length of the fore-end.

The base rifle weighed six pounds, four ounces without an optic or mounts. With a Zeiss Conquest V6 3-18x50mm mounted in Talley lightweight bases, the overall package came to seven pounds, 13 ounces. The whole package balanced very well and would be pleasant to carry in steep terrain.

There’s little doubt that this rifle was built using top-quality parts. AllTerra didn’t just select the best components that it could source, though. It also deviated from well-established machining techniques in hopes of building a more accurate rifle.

On most bolt-action rifles, barrels are mated to the action using threads. A turned-down section of the barrel at the breech end called the tenon is threaded to match the threads on the receiver. When the barrel is torqued into place on the action, proper headspace is established.

I know from building my own bolt-action rifles that the alignment between the threads, the chamber, the bolt face and the receiver ring can all be critical factors in accuracy as well. To that end, AllTerra added a few steps to the barrel fitting process. Two sections of the tenon, one ahead of the threads and one behind, are turned to a specified diameter. These “seating rings” interface precisely with sleeves in the receiver.

Using this method, the barrel not only is threaded into place, but also there’s press-fit contact at both ends of the tenon. AllTerra calls it the Dual-Lock Barrel Seat. If any other builders are using such a method, they are not advertising it. AllTerra claims this design provides superior harmonics, making the rifle less sensitive to various types of ammo.

Fitting the barrel is one thing; cutting the chamber is another. Chamber-to-bore alignment is one of the most critical elements of accuracy. AllTerra’s standard is to coaxially align the bore to within 0.0001 inch before cutting the chamber. Chambers are then drilled and bored before the finishing reamer cuts to the final dimensions. This helps prevent the reamer from wandering as it cuts its way down the bore. It is a time-consuming process, but it pays big dividends on the range.

The innovation doesn’t end there. Beyond excellent accuracy, AllTerra wants its rifles to be reliable in the field. The same ultra-tight tolerances that are conducive to accuracy can often be detrimental to reliability.

Practically speaking, if two parts fit together perfectly the tiniest bit of dust, dirt or grit will gum up the works. Since it’s impossible to avoid such things in the real hunting world, clearances must be built in to allow for environmental debris. The bolt’s profile is full size at the front and rear, where it locks into the receiver, but it’s relieved 0.050 inch toward the center of the bolt body to provide such a clearance. Spiral flutes cut into the bolt also give debris a way of migrating out of critical areas.

The action lugs on the Convergence are conical and lock securely into the elliptical raceway on the receiver while allowing additional tolerances where needed. Finally, the bolt body is coated in nickel boron, a super-slick and corrosion-resistant finish.

The base price for the Mountain Carbon Hunter is $6,250. According to the custom configurator on AllTerra’s website, my rifle as tested would retail for $6,550. Adding the Zeiss optic would bring the total up to $8,449.

While $6,550 is nothing to sneeze at, it is comparable to the price of rifles built by competing companies. With this price comes an explicit guarantee of both accuracy and reliability. AllTerra guarantees that rifles will shoot sub 0.5-m.o.a. three-shot groups with premium factory ammunition and sub 0.25-m.o.a. groups with AllTerra Arms’ own handloads. It also pledges that the rifle will cycle in all conditions and will show no significant change in accuracy when shooting different bullet weights.

I tested the Mountain Carbon Hunter with three different hunting loads: AllTerra’s own handloads that used a 143-grain Hornady ELD-X bullet, Hornady’s new Outfitter 130-grain CX load and a 140-grain Berger load from Gunwerks.

The test rifle came with a test target showing two three-shot groups with an average of 0.17 inch shot on two different dates by two different shooters. I have no reason to doubt the veracity of those targets, but I was incapable of shooting groups that tight with this rifle.

My best results came with AllTerra Arms’ own ammunition and averaged 0.48 inch. That is absolutely nothing to sneeze at, and I would happily hunt with this rifle and load all day long.

I have yet to encounter a hunting scenario where the ability to shoot a 0.25-m.o.a. group was necessary. That said, I was unable to shoot the rifle to a level that would meet the company’s strict accuracy guarantee with this optic and any of the three loads I had access to. As for the other elements of the guarantee, I can report that point-of-impact shifts were minimal between the three ammo types, and reliability was 100 percent.

This is an obviously well-built and well-thought-out rifle. I can find no flaws with its construction or performance. It is light and portable without losing practical shootability, and the fit and finish are excellent. In this chambering, this Mountain Carbon Hunter could be a do-it-all rifle for all but the largest of North American game. At this price point, it’s not a rifle for everyone, but the premium components and quality construction displayed throughout come at a premium.

Allterra Arms Mountain Shadow Carbon Specifications

• Type: Bolt-action centerfire
• Caliber: .22-250, 6mm Creedmoor, 6.5 Creedmoor, 6.5 PRC (tested), 7mm PRC, 7mm Rem. Mag., 7mm Rem. SA Ultra Mag, .280 Ackley, .28 Nosler, .308 Win., .300 WSM, .300 Win. Mag., .300 PRC, .300 Rem. Ultra Mag, .30 Nosler, .33 Nosler
• Capacity: 3+1
• Barrel: 20 in., 1:8 twist, threaded 5/8x24, muzzle brake
• Overall Length: 41 in.
• Weight: 6 lb., 4 oz.
• Finish: Graphite Black Cerakote
• Stock: Pillar-bedded synthetic
• Sights: None; drilled and tapped for scope
• Safety: 2-position rocker
• Trigger: TriggerTech Primary single-stage, 2.1 lb. pull (measured)
• Price: $6,550 as tested; $8,449 w/optic
• Manufacturer: AllTerra Arms, AllTerraArms.com