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Big Bore Upgrade: Should You Hunt Dangerous Game with an AR-15?

Big Bore Upgrade: Should You Hunt Dangerous Game with an AR-15?

 It's no longer news to anybody that during the past decade the AR-15 platform has become a mainstream American hunting rifle. But while deer hunters, predator hunters and varmint shooters have taken to the AR platform by the tens of thousands, you'll still get raised eyebrows if you start talking about an AR-15 as a dangerous-game rifle. After all, it was designed for the puny .223/5.56mm, right? And while it may be just fine if adapted to more effective deer cartridges such as the 6.8mm SPC or .30 Remington AR, it's certainly not suited for the type of heavy-hitting cartridge you'd take into the thickets after a wounded bear or sharp-tusked boar, right?

Think again. When chambered for bigbore thumpers such as the .450 Bushmaster, .458 SOCOM or .50 Beowulf, the AR-15 is as effective a dangerous game-stalking tool as any other rifle ever devised. In such situations, there's a lot to be said for having a full magazine of instant-follow-up semi-auto heavy-bullet shots at your disposal. Been there, done that. Let's take a quick look at what these big-boy AR cartridges have to offer.


The straight-taper .450 Bushmaster cartridge was originally developed as the .45 Professional by Tim LeGendre of LeMag Firearms and is now licensed to Bushmaster Firearms under the .450 Bushmaster name. LeGendre designed the load to be used in the standard AR-15 platform, using modified standard AR-15 magazine dimensions with modified single-stack followers and slightly altered upper receiver/bolt assemblies. The overall cartridge matches the .223 Remington at 2.250-inch length. The .450 Bushmaster upper receivers readily interchange with standard AR-15 lower receivers, so with a simple receiver swap a shooter can handle a prairie dog filed in Wyoming or the bear thickets of Alaska. And thanks to the AR-15's gas system, recoil is much more of a push than the shoulder slap the same cartridge delivers in a bolt-action rifle.

LeGendre came to the basic idea from the "Thumper" concept first espoused by the legendary Col. Jeff Cooper, who had envisioned a .44- or .45-caliber cartridge in a semiautomatic rifle that could provide one-shot kills on big-game animals out to 250 yards. At the time he was writing, Col. Cooper was not an AR-15 fan, as it was then limited to .223 Remington/5.56x45mm NATO cartridges. I'd imagine he'd feel differently if he'd lived to see this one in action.

Original .450 Bushmaster commercial ammo development was done by Hornady at Bushmaster's solicitation, and in the process the length of the .450 Bushmaster case was standardized at 1.700 inches instead of the 1.771-inch length of the .45 Professional in order to accommodate Hornady's 250-grain pointed SST-ML Flex-Tip bullet. The resultant Hornady load develops 2,200 fps velocity and 2,686 ft-lbs muzzle energy from a 20-inch barrel. Commercial .450 Bushmaster ammo is now also available from Remington. Ballistically, the cartridge's trajectory is remarkably flat out to 200 yards. When zeroed at 150 yards, trajectory rise is approximately 1.75 inches at 100 yards, with only a 21/2-inch drop at 200 yards. It is also remarkably accurate, thanks to the free-float barrel/handguard system used on production-grade .450 Bushmaster rifles.

I've hunted European boar in the thickets of South Carolina with the Hornady .450 Bushmaster load and dropped a massive 375-pounder at 25 yards with a single full-penetrating chest shot. The bullet crashed through the heavy cartilage shield of both shoulders, and he collapsed in his tracks. Thumper, indeed.

.458 SOCOM

Although not yet widely known outside the community of AR enthusiasts, the .458 SOCOM has actually been around for about a dozen years. It was originally developed by Maarten ter Weeme of Teppo Jutsu as a response to the same desire for more power that gave rise to Col. Cooper's Thumper notion. And like Tim LeGendre, Ter Weeme created a bigbore AR-15 cartridge that functions in existing unaltered AR-15 .223 magazine bodies, requires zero modification to standard-production AR-15 lower receivers and needs only minimal modification to the uppers.

Based on an uncut preproduction form of the rebated .50 Action Express parent case, the .458 SOCOM is bottlenecked to .458 caliber, unlike the straight-taper .450 Bushmaster. This because of ter Weeme's view that bottleneck cases generally feed more reliably in self-loading firearms than do straight-wall cases. The .458 SOCOM is standardized at 40mm (1.575 inch) length and allows a Barnes 300-grain X-Bullet spitzer to be seated to function in a standard .223 magazine. The case diameter fills the magazine completely, so it works as a single stack with a standard .223 follower — three rounds in a 10-round .223 magazine, seven in a 20-round magazine and 10 in a 30-rounder.

In single-stack configuration, big-game cartridges (right) fit perfectly within standard AR-15 magazine dimensions.
This Bushmaster .450 upper on a Remington AR-15 lower receiver is race-ready for dangerous game.
Big, bad and AR-friendly (from left): .223 (for comparison), .450 Bushmaster, .458 SOCOM, .50 Beowulf.
One shot, one big boar: The author took this 375-pounder with a single Hornady 250-grain SST-ML FTX from his .450 Bushmaster.

The case has a rebated-rim diameter at standard .308 Winchester dimensions to allow more strength in the AR bolt face, making it more adaptable to existing .308-caliber AR bolt designs and to make the cartridge applicable to custom bolt-action manufacture. Depending on load, the resulting round can launch a 300-grain bullet at about 2,000 fps from a 16-inch carbine barrel at relatively low (35,000 psi) pressure. In terminal performance, the .458 SOCOM is roughly the same as the higher-pressure straightwall .45-caliber .460 S&W Magnum with similar bullet weights.

Commercial .458 SOCOM ammunition is currently available at a variety of specialty ammo makers in bullet weights ranging from 300-grain JHP to 500-grain hardcast loads.

I've used Rock River Arms LAR-458 on Texas boar and have been very impressed with it. My 300-grain JHP handload averaged 11/2 inches at 100 yards for five-shot groups (at 1,989 fps), and I was surprised how comfortable and controllable it was, even when practicing rapid fire. Set up in cover 88 ranged yards from a feeder placed to bait feral hogs that were overwhelming a frustrated rancher, the shoulder shot that took my 250-pound boar slammed him to the ground so quickly that I actually thought I'd missed when I blinked from the shot and saw the big sow that had been standing directly behind him running away. I can't imagine a much better full-magazine load to have in an AR-15 if I were in a thicket face-to-face with an angry, wounded animal.


At the biggest end of the bigbore AR-15 scale, the .50 Beowulf was likewise developed by Alexander Arms for use in a slightly modified upper receiver and standard-dimension magazine well. Like the .458 SOCOM, the .50 Beowulf was developed from the .50 Action Express parent case and employs a rebated rim, sized to match the 7.62x39mm and 6.5mm Grendel rounds (another Alexander Arms invention). The case body is similar in dimensions to the .500 S&W Magnum revolver cartridge, but is slightly longer. Unlike the .458 SOCOM, it is not bottlenecked but is tapered for smooth feeding.

Typical commercial-load bullet weights (with Alexander Arms ammunition) are between 300 and 400 grains. Load pressures are within the 33,000 psi limits of the AR-15 bolt system. Its ballistics are essentially the same as a standard .45-70 Government (itself no slouch as a bear or boar load), generating 2,010 fps and 2,916 ft-lbs with a Speer 325-grain HP. That's notably more than a 440-grain .500 Magnum load. And with hard, nondeforming bullets, its penetration is impressive. The heavy .50-caliber bullets are not easily deflected, and monolithic solids will penetrate quarter-inch standard steel plate at 25 yards. And it still doesn't kick much more than a carbine-weight .308 bolt gun.

Anyone who still thinks the AR-15 is merely a "poodle-shooter" owes it to himself to take the the time to try one of these thumpers.

Power plus precision: The author's pet handload for this LAR-458 punched this very impressive 100-yard cluster.

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