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Using a 12-inch Big Horn Armory 500 Auto Max for Defense

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Big Horn Armory, based in Cody, Wyoming, is no stranger to building large-bore rifles. In RECOIL we’ve reviewed a modified .45-70 and recently, a 500 Auto Max both built around AR receivers. But now they’ve outdone themselves, with a lighter and handier “pistol” version sporting a barrel length of a mere 12 inches and a weight below 7.5 pounds.

Features and Details

Though it may look like it’s the same gun you bought for your granddaughter, there’s a lot more going on under the hood. Much like other big-bored ARs such as the .458 SOCOM and .50 BEOWULF, the Big Horn 500 Auto Max can feed from a regular 5.56mm AR magazine in a pinch. However, it ships with a magazine modified in a manner to ensure reliability. The feed lips are truncated, there’s a huge cutout on the front to aid in feeding, and the original follower has been replaced with one more suited for the Tyrannosaurus projectiles.

The 500 Auto Max round itself is a rimless version of the S&W 500, which makes this 12-inch gun the most powerful short range rifle in the world! In a perfect situation, you could just use shells from your 8.38-inch barrel Model S&W 500 concealed carry gun in it. But alas they aren’t swappable unless a lathe is involved.

Unlike many other wildcats, Buffalo Bore produces three different factory loadings: 375-grain JHP, 400-grain JFN, and a 440-grain hard cast for the really big critters and criminals.

Basic takedown is the same as any other Mattel rifle.

The folks over at Big Horn Armory claim that they use a 7.62 NATO receiver set because the round needs the longer stroke for reliability, even though the magwell is sized for the quaint and diminutive 5.56mm. I truly wish the Big Horn Armory 500 Auto Max pistol was based on a more battle-proven design like the M1A instead of a gun that sh*ts where it eats. The heavier, more powerful AR-10 style is used to contain the raw power 500 Auto Max provides. Also missing on the Big Horn receiver is the forward assist you’d normally need for a jammomatic 5.56mm poodle shooter.

The Big Horn Armory 500 Auto Max pistol comes with an adjustable gas block, which we immediately turned to full-bore to ensure functioning with the finicky AR design.


Many people these days prefer to use fancy-and-unreliable new red dot sights, such as the C-More and Aimpoint 2000, but as one of my mentors once said, “Red dots are fine, but 10 minutes after the power goes out, the man with iron sights is king.” Bearing this in mind, I attached a carry handle rear sight and a fixed front sight for the utmost in reliability. There are no weird batteries to die, and when the EMP hits there’s no dot to fry.

Yes, the smaller carry handle does look strange with the longer receiver, but what doesn’t is the piece of mind knowing you have dual apertures for both fast and precision work.

Flashlights on guns are all the rage, but I’ll stick to using a red light in my weak hand when not home, as to not highlight myself as a target to the enemy. But in my own home? Anyone breaking in is up to no good, and therefore is a valid target.

Because Uncle Sam currently calls this a “pistol” we didn’t have any buttstock options. We’re told that if you want Federal agents sniffing around your bug-out location you can get a special license, a process I’m told requires years and even a DNA sample. With that in mind, a pistol brace is just fine.

At the Range

To really shake out the 500 Auto Max I headed to my local range.

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