Big Bore Upgrade: Should You Hunt Dangerous Game with an AR-15?
August 26, 2013
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.
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 followerâ€”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.