Firearm designers are working overtime in their quest to expand AR roles via caliber enhancement beyond typical AR-15 5.56x45 mm NATO and AR-10 .308 Win. chamberings. The urge to expand beyond these standard calibers, while maintaining AR ergonomics, has led to interesting cartridge and platform creations. Combine this with another phenomena associated with non-traditional pistol models resulting from adding a brace in lieu of buttstock and the stage is set for some intriguing platforms. The Big Horn Armory (BHA) AR500 pistol chambered in .500 Auto Max is an excellent example of this.
The Big Horn Armory AR500 pistol chambered in .500 Auto Max
For individuals that have no legal access to NFA Class 3 Short Barrel Rifles (SBR), the braced pistol may well be the closest they can get to achieving such a compact rifle-caliber package. AR type pistols are dominating this genre as firearms featuring shorter than 16” barrels with only a buffer tube protruding from the rear of the receiver.
The Big Horn Armory AR500 muzzle brake does a nice job of taming, also note the free-floating handguard.
Big Horn Armory based its AR500 on the AR-10 platform with intent of creating the most powerful short-range, semi-automatic AR platform in the world. The initial Big Horn AR500 model was a rifle, but the company decided to introduce a pistol version as well. The AR500’s bolt head is modified to accommodate the .520” rim of the .500 Auto Max cartridge. Big Horn engineers then determined optimal location for the extractor and ejector for proper function.
The 10” 1:24 twist barrel is stainless-steel with a nitride surface-hardening and corrosion-resistant treatment. The Rockwell C hardness rating of the barrel is 82. It comes with a muzzle brake threaded on and features an adjustable gas block to ensure reliable function, no matter what load is chosen for use.
The AR500’s bolt carrier group is nickel-boron coated offering less friction during operation and ease of cleaning.
The AR500’s handguard is free-floating and M-LOK compatible. The AR500’s bolt carrier group is nickel-boron coated offering less friction between surfaces and easier cleaning in that carbon fouling doesn’t adhere as much. The AR500 features an ambidextrous charging handle, safety selector and bolt catch. The AR500 also features a gem of a trigger, with a pull weight measuring in at 3 to 3.5 lbs.
.500 Auto Max rounds load single stack into an AR-15 style magazine for the AR500.
An interesting detail with BHA AR500 is its use of AR-15 size magazines, even though the AR500's receiver is based on AR-10 size profile. The modified AR-15 magazines are single-stack and provide better feed geometry for the sausage-size, straight-wall .500 Auto Max cartridge. Five- and nine-round capacity magazines are offered by Big Horn Armory. The typical AR-15 follower is modified and a stout 30-round magazine spring is fitted under the follower to make sure the next round is ready for loading as the bolt comes forward.
115 grn. 9 mm (left), 440 grn. Buffalo Bore Hard Cast .500 Auto Max (center) and 140 grn. 6.5 mm Creedmoor (right).
The .500 Auto Max is the brain-child of Greg Buchel, President of Big Horn Armory, in collaboration with Tim Sundles of Buffalo Bore Ammunition. The .500 Auto Max is essentially a rimless .500 S&W Magnum cartridge. It can be reloaded with the same dies, shell holders and load data. However, a taper crimp is required, due to the 500 Auto Max head-spacing off the case mouth versus the rim. The .500 Auto Max can chamber and fire in any revolver or single-shot chambered for the .500 S&W, yet the reverse is not true. Due to taper crimp with the .500 Auto Max, revolver users must pay heed to cartridges shifting forward in the cylinder after a few shots due to recoil.
The modified AR-15 magazine is single stack and provides better feed geometry for the sausage sized straight wall .500 Auto Max cartridge. Five and nine round capacity magazines are offered by Big Horn Armory.
The .500 Auto Max generates unprecedented stopping power at short-to-moderate ranges out of the BHA AR-500 pistol. The AR-500’s 10” barrel length is optimal for the .500 Auto Max cartridge’s performance. With 350 to 440 grn. loads from Buffalo Bore and Steinel Ammunition generating muzzle velocities of 2100 f.p.s. to 1760 f.p.s. respectively, a 100 yd. zero will give a relatively flat trajectory out to 150 yds.
That is 1” high at 50 yds. zeroed at 100 yards, dropping 4.5” at 150 yds. and 13.5” at 200 yds. The .500 Auto Max’s heavy, large-diameter bullets make it well-suited for use against large hogs or even a charging bear.
The AR500 bolt head had to modified to accommodate the .520” rim of the .500 Auto Max cartridge. Big Horn engineers then figured optimal location of the extractor and ejector for proper function.
A Buffalo Bore 440 grn. Hard Cast load with a velocity of nearly 1,800 f.p.s. generates close to 4,000 ft.lbs. of muzzle energy. 350 grn. jacketed .500 Auto Max loads pushed along at 2,100 f.p.s. are deadly effective on softer skin animals. .50 caliber bullets weighing 400 grns. plus offer excellent sectional densities required for hunting heavier North American or African dangerous game. Dangerous big game hunters know that ft.lbs. should not be only criteria for cartridge selection. Bullet diameter, shape and construction play important roles as well and the .500 Auto Max checks all these boxes.
Ammunition for the .500 Auto Max is currently available from Buffalo Bore Ammunition and Steinel Ammunition. Multiple loads exist including hard cast, jacketed hollow point and solid brass.
A Crimson Trace CTL-5108 1-8x28 mm scope with illuminated reticle was used with the BHA AR500. The Crimson Trace 1-8x uses high end Japanese ED glass for clarity and light transmission. The custom designed SR1-MIL advanced reticle is fully illuminated and offers a quick acquisition outer ring that vanishes when magnification is increased. The optic was attached with a Wheeler Engineering 34 mm one-piece cantilever mount. Designed specifically for use with the AR-15 platform, the Wheeler mount allows the optic to be mounted farther forward on the upper-receiver to provide correct eye relief. Centerline height from the top of the rail is 1.4”.
A Crimson Trace 1-8x CTL-5108 optic with Illuminated Reticle was used with the Big Horn Armory AR500.
The offset six-screw design provides increased clamping force to keep the optic in place through hard recoil and the integrated articulating anti-cant mechanism helps keep the rifle level for your long distance shots. The Crimson Trace 1-8x is designed for both instinctive close-range low-magnification situations with variable intensity red illuminated reticle, yet still allows shooters to engage targets with greater precision at longer ranges thanks to the 8x capability. The Crimson Trace CTL-5108 1-8x power range and reticle configuration eliminates the need for using multiple optics as scenarios change. The BHA AR500 with Crimson Trace optic produced consistent 2” or better groups at 100 yds.
A Crimson Trace CTL-5108 1-8x28 mm with illuminated reticle was used with the Big Horn Armory AR500. The Crimson Trace optic was attached via Wheeler Engineering 34 mm one-piece cantilever mount.
The BHA AR500 pistol with its portability is intended for stalking or still hunting forays. This translates into fluid, off-hand shots at game and not off rests or bipods. If lucky the hunter will be able to adopt a kneeling or sitting position in lieu of offhand. This was simulated during testing and evaluation at Echo Valley Training Center (EVTC) by setting up clay pigeons at various ranges and then shooting from sitting, kneeling and standing positions.
Another twist is to have a companion pick the target and shooting position while shooter engages as designated as quickly as possible. The BHA AR500 proved devastating against range vehicles located on EVTC’s stepped berms. The .500 Auto Max loads had no issue penetrating windshield or car bodies to hit steel popper targets located inside.
A 50 yd. target with the Big Horn Armory AR500 pistol. The .50 caliber holes appear in stark comparison to the .22 caliber also present on the paper.
Field testing consisted of multiple runs on EVTC's Jungle Walk Range. The ability to move through its varied terrain and engage randomly placed targets hidden within cover suited the BHA AR500's evaluation perfectly. Ranges involved were from 35 to 150 yds. with multiple shots fired at most of the targets.
The low 1x setting on the Crimson Trace optic allowed for a wide field of view and quick target engagement. The illuminated reticle simplifies dusk or dawn aiming situations. The BHA AR500 proved to hang well and was very manageable in getting into and out of field shooting positions.
Big Horn Armory AR500 pistol being used in field expedient firing position at Echo Valley Training Center.
The AR500 pistol’s blade brace inspired some concern when initially in terms of recoil management. While stout, the BHA brake does a good job taming rearward shove. Anecdotally, the AR500’s muzzle brake tames felt recoil into about the 20-ga. shotgun realm for reference. Big Horn Armory has created its own AR sub-category with the AR500 chambered in .500 Auto Max. It is difficult to compare the BHA AR500 pistol to any other cartridge and platform combo on the market.
The ability to reliably engage targets out to 200 yds. with great terminal effect cannot be overstated. The inherent familiarity most have with the AR platform, not to mention its top-notch ergonomics, validates Big Horn Armory’s decision to use an expanded caliber. The BHA AR500 pistol pushes the AR operating envelope a step further in its evolutionary path. For more information on the Big Horn Armory AR500 visit bighornarmory.com.
Specifications Caliber: .500 Auto Max Barrel: 10" chrome moly hammer forged Overall Length: 32.25" Weight: 8.5 lbs. Action: Semi-automatic Capacity: Detachable five-round magazine (nine-round version available) Suggested Price: $2199