Five things to know about the .500 Auto Max (VIDEO)

01/10/19 10:00 AM | by

.500 Auto Max rounds lay in wait. The Big Horn Armory AR500 is an AR-10 platform of a beast, firing our 350-450 grain bullets accurately and with ease, more than capable of taking down any game in the country. (Kristin Alberts/

The catch phrase for the new AR500 in .500 Auto Max from Big Horn Armory may be the best of the year. “It can handle anything from prairie dogs to Pachyderms to Peterbilts.” That’s some serious stopping power in a platform weighing less than ten pounds. It’s time we learn about that round.

  1. The .500 Auto Max is the brainchild of Greg Buchel, President of Big Horn Armory in Cody, WY in conjunction with Tim Sundles of Buffalo Bore Ammunition in Salmon, ID. Both gun and ammo were launched in 2018.  Big Horn is known for building custom-grade, big bore rifles. Likewise, Buffalo Bore is one of the best in the industry for producing premium, hard-hitting, heavy hunting loads.
  2. The .500 Auto Max packs some serious wallop. Per Big Horn Armory, “Three pulls of the trigger puts 50 BMG power on target” in an AR-10 platform with reliable extraction. Buffalo Bore states that as of early 2019, “the .500 Auto Max is the most powerful cartridge made for use from any AR platform.”
  3. Only Buffalo Bore and Underwood produce the ammunition. Starline makes and sells the brass for reloaders. Buffalo Bore is clearly in the lead here, working directly with Big Horn to tailor rounds to the guns. The .500 Auto Max launches bullets from 250 to 700 grains, with many options yet to come, including subsonic rounds. Big Horn warned us to beware early loads from Underwood which were “loaded very hot and dropped primers.” That issue seems to have since been rectified.
  4. The .500 Auto Max is essentially a rimless .500 S&W Magnum. Reloaded with the same dies and shell holders, the Auto Max uses the same load data as the .500 S&W Mag, save for requiring a taper crimp instead of the standard roll crimp. This is due to the Auto Max headspacing off the case mouth instead of the rim.
  5. Big Horn Armory is the original and only company building a firearm for the Auto Max.  In fact, they build two: the AR500 Rifle and a just-announced AR pistol as well. The rifle retails for $1,999. Our test rifle wears a 1:24 twist 18 inch Barrel, adjustable gas block, picatinny rail, adjustable buttstock, flash suppressor, and ships with a five-round magazine.

For more info on both the .500 Auto Max chambering and the AR500 platform that fires the round, check out our review at If you’re wondering what the .500 Auto Max has to offer over, say the .50 Beowulf or other large caliber AR-15-based rounds, that and other details can be found there, as well as plenty of big hunks of lead going downrange.

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