Interview With the Developer of 500 Auto Max

   11.19.20

Interview With the Developer of 500 Auto Max

Not long ago, I told AllOutdoor readers about my introduction to the .50 caliber guns of Big Horn Armory. Since then, I’ve been in touch with Greg Buchel (pronounced Buckle), BHA’s founder/owner. He filled me in on the inspiration and design process for the 500 Auto Max cartridge, as well as the backstory on his semiauto guns chambered in 500 Auto Max. While the cartridge and guns are based on existing models (as in the 50 S&W cartridge and Stoner and lever platform rifles), there was an inventive process behind each. Inasmuch as I find gun inventions fascinating and surely I’m not alone, it seems worthwhile to share.

This interview focuses on cartridge development as well as the two semiautos made by Big Horn Armory. Here, from Buchel himself, is how they came to be.

Buchel fires his Model 89 lever action rifle.

ALLOUTDOOR: What came first, the idea for a 50 S&W-type semiauto, or the cartridge itself?

Buchel:  There was a pattern among my customers; most are guys in their 50s or 60s, like me. I wanted to draw a younger customer base, and that meant going the direction of the AR. Ultimately, the cartridge was completed first. We tried sticking the 500 S&W in a box magazine, utter failure. The solution was pretty simple. Once I determined that the rim was perfectly sized to lock solidly in the the extractor groove, the rim had to go. Cartridge design was complete. Tooling for loading the cartridge was simple. Standard 500 S&W dies and shell holders worked perfectly. The only setup change was adjusting the crimp die to provide a taper crimp instead of the usual roll crimp.

50 Auto Max with Starlite headstamp

ALLOUTDOOR: Did you patent the cartridge?

Buchel:  No patents, trademarks or copyrights on the 500 Auto Max. It is completely public domain. That’s on purpose to make it easier for ammo companies to load the cartridge. Also, to let gun manufacturers copy it, if they so choose. 

I grew up in the software world of the 70’s & 80’s. With very few exceptions, the companies that thrived put few restrictions on their products, unless they had massive advertising and R&D budgets.

Once the cartridge was complete, I enlisted Tim Sundles from Buffalo Bore to load factory ammo and Robert Hayden from Starline to make the brass. They were very enthusiastic about this since they are both big bore guys.

Buffalo Bore is one of two companies providing 500 Auto Max factory loads.

 ALLOUTDOOR: Now there’s a load, but what about the rifle to fire it?

Buchel:  The rifle was a can of worms, relatively speaking. We knew we wanted to keep the rim size as big as possible to simplify reliable extraction. This made the AR10 platform a necessity. The next issue was the magazine. We started with AR10 – SR25 mags. They worked okay in double stack since the case diameter was similar to the 308 Win. We had to redesign the follower to fit and create a filler insert for the front of the magazine to integrate with the follower and form a ramp to move the 2.250″ cartridge up into a feeding position in conjunction with the release from the feed lips. 

These two changes required about $100,000 in tooling costs for plastic injection molded parts. This was not in the budget. I saw that the AR15 was nearly ideal for the 500 Auto Max. 2.250″ OAL vs 2.290″ OAL for the 5.56 NATO. No need for fillers and we got a simpler single stack. The search for durable magazines that would not allow the feed lips to spread and change the release point. Only steel AR15 magazines worked and only a few manufacturers made thick enough sidewalls to be durable. 

AR15 magazines in an AR10 platform required an insert in the mag well and an integral ramp for feeding. We designed this into the lower receiver. The upper receiver required only minor relief in the ejection port to allow the large case mouths to eject cleanly. The last two modifications were opening up the bolt face to allow our case rim to fit and modifying the extractor to mate with the 500 Auto Max rim for solid extraction.

The rest was finding a buffer and spring combination that worked with the loads, pressures and recoil impulse. Mostly trial and error with empirical testing.

Big Horn Armory AR pistol chambered in 500 Auto Max

One may wonder why anyone would need a semiauto that fires a half-inch bullet. It’s not a bad question. Buchel understands the importance of sure, humane kills on large African game animals, which can be notoriously tough to penetrate. There’s a lot to be said for making an entry wound that’s as large as many other big game bullets at full, terminal expansion. And as with some other very large calibers, the 50 Auto Max and its parent cartridge, the 50 S&W, consistently provide a stunning effect on large game that allows for closing distance and/or a finishing shot, if necessary. And then there’s the simple fact that it’s just plain fun to shoot the largest available chamberings in an AR or lever gun.

As I experienced when testing Big Horn Armory’s guns at a gun writers’ conference, with the exception of the AR pistol, recoil is surprisingly manageable. That puts these guns in the realm of interest for a wide variety of shooters, not only in age but in stature.

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