Big Horn Armory AR500: 3,700 ft-lbs of Big Bore Record-Breaking Awesomeness (Full Review)

You’ve never seen an AR like this before…

I don’t often get the chance to review a record-breaking firearm. The usual suspects in my T&E lineup – bolt action .308’s, semi-auto CCW’s, and pump-action shotguns – are functional and fun to shoot, but few are as unique as the AR500 from Big Horn Armory.

The AR500 is, according to the company’s claims and my own research, the most powerful short-range semi-auto rifle in the world. Chambered in the .50-caliber 500 Auto Max cartridge, the AR500 packs a wallop in a modified AR-10 platform. Its semi-auto action is perfect for big and dangerous game hunters, and it offers the maneuverability and customizability inherent in the AR platform. Combined with Buffalo Bore’s 350, 400, and 440 grain loads, the AR500 is ready to bring down, quite literally, any kind of critter you’re hoping to hunt.

First, spec sheet/feature list.

  • 1:24 twist
  • 18″ Barrel
  • Adjustable gas block
  • Full Picatinny rail
  • M-Lok handguard
  • Adjustable Buttstock
  • Muzzle brake
  • Thread Pitch: 3/4×28
  • Carbine Length Gas Tube
  • Weight: 9lbs, 1.7oz unloaded
  • 5-round magazine
  • Hard plastic case
  • MSRP $1999.00

500 Auto Max?

Left to right: 300 Blackout, .308, 500 Auto Max, 5.56

You’ve never heard of this cartridge because it didn’t exist before Big Horn Armory began developing the AR500. As the folks at Buffalo Bore Ammunition explain, Greg Buchel, the owner of Big Horn Armory, approached the ammo company for help developing a .50-caliber cartridge suitable for the AR-10 platform.

The result was the 500 Auto Max, a reduced-rim 500 S&W currently available loaded with three projectiles: a 350 grain jacketed hollow point, a 400 grain jacketed flat nose, and a 440 grain hard cast. Buffalo Bore plans to expand their offerings in the coming months using everything from 600-grain projectiles to light, fast JHP rounds. The company was kind enough to send me samples of each load currently in production, and they sell boxes of 20 on their website for $67.00 ($3.35/round).

Left to right: 440g hard cast, 400g JFN, 350g JHP

If that sounds a little steep, keep in mind that once you accumulate a collection of AR500 brass, you can reload this ammunition for a much lower cost. According to Buffalo Bore, 500 S&W load data can be used to make this cartridge, though they warn that “care must be given to powder selection to keep from gumming up the AR action.” You can also chamber and fire AR500 ammo in any single-shot or revolver chambered in 500 S&W (though the reverse is not true – don’t try shooting 500 S&W in your AR500). One caveat: Buffalo Bore warns that because AR500 cartridges headspace on the case mouth, they lack the roll crimp necessary to stop the bullet from jumping forward when subjected to heavy recoil. So, if you use AR500 rounds in a revolver, it might be wise to shoot them one at a time.

However you choose to use the cartridge, you’ll smack whatever happens to be downrange. In my testing, the 350-grain projectile average 2207 fps at the muzzle, the 400-grain averaged 1960 fps, and the 440-grain averaged 1838 fps. To provide some perspective, I compiled a chart listing a variety of common cartridges chambered in the AR platform. I’ve included both kinetic energy (foot-pounds) and John Taylor’s “Taylor Knock Out” number. Unlike the kinetic energy formula, the Taylor KO formula accounts for bullet diameter and is generally considered a better way to compare the effectiveness of different rounds against big game at certain velocities (the higher the number, the better).

CartridgeBullet Weight (g)Muzzle Velocity (FPS)Foot-Pounds of EnergyTaylor KO
300 BLK1252200134411
.308 WIN1682600252218
300 WM1852900345622
450 Bushmaster2502200268735
50 Beowulf3501820257545


None of these numbers account for bullet construction, and a 300 WM will be more effective than a 450 Bushmaster, for example, at longer distances. Still, it’s clear from both kinetic energy and TKO that the AR500 makes a convincing argument as the most powerful semi-auto short-range rifle on the market.

The 500 Auto Max’s maximum effective range will depend upon the target, the shooting conditions, and, of course, the shooter. I won’t pretend to be a terminal ballistics expert, but my suspicion is that this cartridge can push a projectile at lethal velocities far beyond its accuracy potential. Based on the results of my testing (below), you can confidently put rounds in the kill zone out to about 400 yards, depending, again, on the target.

Buffalo Bore has also published complete data charts on each load (350g, 400g, 440g), which provide tons of helpful information for a variety of muzzle velocities.


The AR500 breaks down like any other AR-10.

But enough about the cartridge. The AR500 feels, looks, and shoots (more on the below) like a $2,000 rifle. Big Horn Armory packed their record-setting long gun with tons of great features, all of which provide either aesthetic or practical (but mostly practical) value. The great-looking Ascend Armory receivers are constructed from 7075-T6 billet aluminum and feature enhanced AR-10 front and rear take down pins, ambi bolt catch/release levers, anti-rotation trigger and hammer pins, and an oversized magwell and trigger guard. The safety selector is also ambidextrous, but the mag release is right hand only. The pistol grip is from ERGO Grip and is totally rubberized.

I think the receivers are sharp, but more importantly, they fit together perfectly. The receivers on the model I tested didn’t exhibit any noticeable movement while still maintaining ease of disassembly.

The receivers fit together without any wobble, and include all the high-quality components you might expect.

You could park a tank in that thing…

The magwell is expanded but also modified to accept the 500 Auto Max magazine.

The bolt is coated in nickel-boron for added reliability. (It was also soaking in gun oil when I received it from Big Horn.)

The massive bolt and bolt carrier group are nickel-boron coated for added reliability. Otherwise, they’ll look familiar to anyone already accustomed to the AR platform. The trigger is excellent—just what you want for a once-in-a-lifetime big-game hunt. It’s crisp, consistent, and relatively light. On the model I tested, the trigger broke cleanly at 4 pounds, 8 ounces.

Moving to the rear of the gun, the Adaptive Tactical buttstock is adjustable and features a healthy recoil pad. The stock works fine, though I found it wobbles quite a bit. The wobble didn’t affect performance, but stock wobble is one of my pet peeves, and I’d wager I’m not alone. The castle nut can be staked to keep it from spinning loose.

The trigger is excellent.

The stock does a great job absorbing the heavy recoil.

The castle nut can be secured using an Allen wrench.

The M-Lok handguard also has Picatinny sections for mounting flashlights and other accessories.

The muzzle brake does a nice job minimizing recoil.

Moving forward, the handguard extends nearly to the end of the barrel and features M-Lok cutouts, a complete top Picatinny rail, and short rail sections on the front and rear at the 3, 6, and 9-o’clock positions. It also includes quick-detach sling mounts on both the right and left-hand sides, which pair with the QD mounts milled into the receiver. Finally, the 18” 416 SS barrel is coated with nitride and topped with a much-needed eight-hole muzzle brake.

Reliability, Accuracy, and Performance

I put a lot of lead downrange the day I tested the AR500.

The AR500 is a reliable rifle, provided the shooter can maintain a firm grip. Much like the 1911, this beast requires a strong hand, and I found that shooting from the prone delivered better results than from the standing or kneeling positions. Greg Buchel, the owner of Big Horn Armory, confirmed my suspicions. He explained that it’s important for the shooter to provide a solid base against which the rifle can recoil. They’ve found that strong shooters using proper technique can run an AR500 without any issues, while other shooters can have trouble using the same firearm.

He also noted that their rifles generally need a 100-200-round break-in period before they’re running at peak performance. If the rifle is still malfunctioning after 200 rounds, the adjustable gas block can be tuned down from fully open to ½ or 1/3, which usually makes the gun run more smoothly.

The gas block can be adjusted to correct cycling problems.

Most of the cases remained round (right) or were flat on one side from hitting the shell deflector (left). A few others were strangely warped, possibly due to extraction issues (middle).

I experienced three failures to extract during the course of my testing, but none while shooting from the prone position. I guess I need to work on my form—or hit the gym. If I planned to keep the rifle long-term, I’d also consider adjusting the gas block.

In terms of accuracy, Buchel said they expect 1.5 MOA groups from the AR500. The groups I shot tended to be larger, though for a rifle of this caliber I’d be happy with anything under 2 inches. I shot these groups from 100 yards using a Caldwell Lead Sled. The wind was minimal, and the temperature was right around 96 degrees.

BulletAverage Velocity (FPS)Smallest Group (in)Average Group (in)
350g JHP22071.82.3
400g JFN19601.82.2
440g HC18383.55.2


350g JHP

400g JFN

440g HC

The 350g and the 400g loads performed well, but my rifle didn’t favor the 440g hard cast bullets. I thought perhaps the barrel was too hot or my scope had lost its zero, so I shot another group with the 400g load immediately after the first 440g group. The 400g group shrank down to normal size, so I ruled out any abnormal rifle or scope malfunctions.

Buchel told me they haven’t tested the rifle with the 440g hard cast load, so they aren’t sure what kind of accuracy to expect. It’ll do its job on a charging bear from 50 yards, but I’d need to conduct more testing before going after game with the 440g.

Shooting the AR500 requires a strong stance to avoid cycling issues. (And yes, I forgot to wear shooting glasses for this picture. Always wear shooting glasses for safety, especially on a big-bore semi-auto like this.)

The rifle handles well. I found it to be somewhat front-heavy, but it’s light enough to land shots in the standing position. Recoil feels much stiffer than a standard AR-10, but the muzzle brake and recoil pad keep it to a manageable level (something akin to a 45-70). The muzzle brake allows for relatively quick follow-up shots, but don’t expect your shot splits to rival the performance from an .308 AR-10.

Central Texas is decidedly lacking in elk, moose, or grizzly bear, so I can’t speak directly to the rifle’s performance against large and dangerous game. But I have found the water jug test to be a decent yardstick for bullet behavior, so I decided to give it a try.

  • The 350g JHP blasted through two one-gallon water jugs, fragmented, and penetrated a third.
  • The 400g JFN blasted through five one-gallon water jugs, opened, and penetrated a sixth.
  • The 440g HC blasted through nine water jugs and lodged in the stone backstop

The 400g round destroyed the first two jugs and continued through the next three until stopping in the sixth.

This is where I found the 440g HC after it blasted through nine water jugs: between two stones I had used as a backstop.

Left to right: 440g HC, 400g JFN, 350g JHP. The projectiles performed exactly as advertised.

The results of the test are consistent with what Buffalo Bore says to expect from each load: 1) the 350g is designed for game up to 600 pounds and will likely disintegrate on big shoulder bones at close range, 2) the 400g is designed for game up to 1500 pounds and will over-penetrate deer-sized animals, and 3) the 440g is designed for animals up to 3000 pounds and will penetrate deeply and straight.

For perspective, I conducted the same test last year using .556, .308 WIN, and 450 Bushmaster. The .556 penetrated two jugs, the .308 penetrated five, and the 450 Bushmaster penetrated four. While water jugs aren’t a perfect stand-in for animal flesh, the test confirmed the expected bullet behavior and suggests how the 500 Auto Max might compare with other AR cartridges in terms of penetration power at close range.


For me, the most exciting benefit of the AR500 is its combination of cartridge and platform. The 500 S&W has been around since 2003, and the AR platform has been in production since the 1950s. Combining the two gives users the power of the 500 S&W with the rapid fire/reload functionality of the AR-10. For decades, anglers have used big-bore revolvers and lever action rifles for bear defense in harsh northern terrain, but the AR500 provides better accuracy and handling than a revolver and faster shot splits and reloading than a lever action. If I’m staring down an angry bear at 50 yards, I want the AR500.

The same holds true for large and dangerous game. If I’m on the hunt of a lifetime in Africa or Canada, fast follow-up shots can ensure the critter won’t get away, and I’ll have a trophy for my efforts (not to mention hundreds of pounds of meat).

From feral hog to cape buffalo and everything in between, the 500 Auto Max out of Big Horn Armory’s AR500 is, in short, versatile enough to take down whatever you’re hoping to hang on the wall.

About the author: Jordan Michaels has been reviewing firearm-related products for over six years and enjoying them for much longer. With family in Canada, he’s seen first hand how quickly the right to self-defense can be stripped from law-abiding citizens. He escaped that statist paradise at a young age, married a sixth-generation Texan, and currently lives in Tyler. Got a hot tip? Send him an email at

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  • Max Mirenda May 1, 2021, 8:38 pm

    I’m looking forward to my delivery date mid May. I also ordered ammo from bi bore in my experience they are highly overpriced on ammo and shipping. They lack customer satisfaction skills so search out other manufacturers.

  • David Whisnant January 25, 2020, 8:30 pm

    From what I have read it will be awesome

  • Gavin July 28, 2019, 7:41 pm

    The Taylor Knock Out factor I find to be fairly erroneous as not all bullets maintain their full bullet weight in penetration so as soon as you have fracturing what should be measured is the amount of average between the starting weight of the bullet and the biggest piece found ( otherwise he’s just have a different crack at KE plus a bullet that is unequal by density of material used so its not great)

    In saying that even already have several 500 S&W rounds that well exceed the TKO of the AR500 round so really shouldnt the test be AR500 Vs 500 S&W? Or do you actually believe that a person will be able to keep the AR500 on target any faster than running a lever for a follow up shot or what about a other actions?.

    • Colin October 24, 2020, 10:49 pm

      As someone who owns a Marlin 1895g 45/70 and a Ruger AR-350 in .350 legend, I can assure you an AR is FAR faster when it comes to follow up shots and maintaining target acquisition, and the extra magazine capacity coupled with the ability to carry multiple magazines is an added bonus. The AR is the superior platform in terms of overall performance. The 1895 is still twice as fun to shoot though IMO, and I would definitely trust my 45/70 over my .350 to stop a bear. But I’d take an AR500 over my 1895 any day when it comes to hiking through big bear country…

    • Rexford L October 6, 2021, 4:13 pm

      The 500 Auto Max IS the 500 S&W Magnum, with just the rim turned down to be able to cycle in the AR platform and using the roll crimp vs taper crimp so anything the 500 S&W can do, the 500 Auto Max can do. The ONLY proviso to this, the AR500 isn’t designed to fire the 700 gr bullets that you can fire in a S&W 500 revolver.

  • J. Smith December 25, 2018, 1:54 am

    I’m only interested in which AR platform .50 cal takes out engine blocks most effectively and is not a 50 big. As was one of the original purposes for the 50 Beowulf in early 2000’s for the GWOT mission.

    Numbers are impressive. Would love to see steel core rounds, yahoo… So, whats the shelf life of an aluminum lower with this?

  • jack November 4, 2018, 5:57 am

    I would use the 440g and heavier loads on zombies, if you line up about 8-10 of them you can shoot straight through all of them! All kidding aside, this about parallel’s my custom Browning model 71 50 Alaskan in performance and would be faster with follow-up shots, besides my Browning doesn’t have a muzzle break and I bet this would be more pleasant to shoot, I’ll be placing an order immediately.

  • MojoMitch November 2, 2018, 11:52 am

    Well, their going in the right direction, as I’ve been wanting large bore knock down type ammo to continue to be progressive in the AR format for years now, but less expensive than this, plus this one looks like it still needs some fine tuning yet. I’m hoping for more progress in the 45 to 50 plus cal ballistics and then building an AR-10 around it with less gas and ejection issues and not roughing up the brass or maybe trying something new in the brass/metal arena and pushing a 440 flat head at minimum for max penetration.
    I also agree with comments from the gentleman about the 308.
    Off/On topic, I’ve got a 2002 Ford Focus, that I purchased a few years back for my son to use to go to college, etc, that I want to turn into swiss cheese with something like this AR someday and post it on YouTube with some of my buddies joining in on the fun. It took me for plenty of dough, worst vehicle that I have ever had and poorly made. A tricky car salesman, who pretended to be a “private owner” that takes cars home when someone calls his cell about his car add. Sneaky deceptive bustard’s, lol.
    Burning or having it crushed wont suffice, so were just going to pretend that it’s a charging brown bear or a rhino and stop it for good, make Bonnie & Clyde’s death car look good, lol.

    Thanks for the article!

    • Shaun January 8, 2020, 10:37 pm

      Being a Mainer I may be a bit biased but definitely take a gander at the Windham Weaponry 450 Thumper. The common complaints of the .450 Bushmaster tend to relate to small gas ports or poorly modified AR mags. Windham’s Thumper cycles lovely and their mags are flawless. They also have an incredible warranty and you can often find the Thumper on sale for $900-1,100.

      This AR500 does have me drooling though, I hope it catches on and more companies start manufacturing the ammo and producing magazines!

  • AJ October 31, 2018, 12:03 pm

    Pretty decent looking piece. Gives us a new term to play with too, “hand-cannon caliber carbine”.

    It’s neat, and may help Magnum hunters save their wrists. But, AR platform .50s have been attempted. The .50 beo was an interesting attempt as well. But doesn’t have much of a following.

  • ms October 30, 2018, 8:08 pm

    Yawn. I will keep my LW .499.

  • David October 30, 2018, 1:40 pm

    I have the Winchester model 70 XTR that shoots 300 Win. Mag. I am very happy with it and it is more than enough rifle for anything I wish to hunt. Ammo cost anywhere from $ 16.00 to $60.00 per 20 rounds. I have no plans of shooting thru 2 or 3 buildings at a time. It cost me $600 when I bought it. enough said.

  • Joe October 30, 2018, 9:48 am

    My AR-10 in .308 should suffice thank you. If the first round doesn’t drop em the second through twenty Back up rounds should do the trick on any any and all big north American game animal from bull moose to T-Rex. And it only cost me $700 bucks to put together and a 20 round box of ammo sells for less than fifteen bucks. But if I ever go after a Diplodocus maybe I might find use for your elephant gun.

  • Mike Cornett October 29, 2018, 4:58 pm

    If you build it, they will come.

    • mtman2 October 30, 2018, 3:27 pm

      Ah yup – they will…likely died in the wool hog hunters that want hogs anchored w/no squealing.

      Likely few will buy once figuring ammo cost…$$$
      Tho wouldmake a backup gun for Grizzz – yet still won’t beat a 12gauge slug at that…

      • Gavin July 28, 2019, 7:51 pm

        BahBow – Fail

        Shotgun slugs (12 gauge) achieve typical velocities of approximately 1800 fps for 1-oz. (437.5 grain) slugs, for an energy of over 3,100 ft-lbs (4200 J)

        500 S&W bullet (22″ barrel) achieve velocities of approximately 1970 fps for 1.1-oz. (450 grain) slugs, for an energy of over 3,879 ft-lbs ( whatever J)

  • MIKE October 29, 2018, 1:28 pm


  • Rally Hammer October 29, 2018, 1:06 pm

    This is the type of AR platform that should be made available to ALL American Sportsmen throughout the United States, Not just outside California. This is a TRUE Hunting Rifle. After Vietnam Everybody wanted an AR Platform rifle because it was The Future of Shooting. As a U.S. Marine I was Trained with the M-14 and later as an 0331 Machine Gunner I carried the M-60 Machine Gun, and as a Squad Leader the M-79 Blooper. I was finally Issued my first M-16 which I Pleasantly found to be a LOT lighter than the M-14 and the M-60 when I became a Weapons Platoon Sgt. The worst misconception from our Representatives on Capitol Hill and American Media is the truth that IF an AR Rifle does NOT have a SELECTOR SWITCH that allows it to Fire MORE than One Round every time the Trigger is Pulled, then “IT IS NOT AN ASSAULT WEAPON”. This New AR-500 is to me an OUTSTANDING Rifle for Hunting, Competition and Defensive Applications. A Machine Gun is NOT the Answer to anything but Combat, take it from me, I Know, Save your Ammo and your Bank Account. Question : Where do I have to Move too Own one ?

  • Grant Stevens October 29, 2018, 12:50 pm

    “My gun’s bigger than your gun!”. Another over-powered, over-priced novelty to impress those with small egos and other appendages. However, it would be great for shooting dinosaurs.

  • The Bearded Pretender October 29, 2018, 12:25 pm

    If the details are anything like the two Custom Big Horns I had made, I’ll pass.
    Very disappointed with the Model 89 in .460 S&W they built for me… Shipped with glue and tape residue
    in the action, the $600 wood upgrade was disappointing and the action catches when cycled.
    Maybe your $4,000.00 gun will work out better for you, mine didn’t.
    And after paying $350.00 for the barrel to be threaded, it shipped with a piece of rubber hose for a
    Thread Protector?! I called and was told the metal protector was $80 bucks…You can’t make this stuff up…
    $80 bucks for a $6 part online!

  • Steve October 29, 2018, 10:23 am

    This should be compared to the .50 Beowulf developed by Alexander Arms the .50 Beowulf has been around for several years and is built on the standard AR- platform. Seems to me that comparing similar rounds would have been more helpful than comparing smaller rounds and traditional rifle calibers.

  • Adam Jeppson October 29, 2018, 9:28 am

    Way cool rifle for sure – but the shot of the bullet between the rocks is a real once in a life time! ..And you included it in the article! Thank you.

    Now, I’ll take two.

  • Steve K October 29, 2018, 7:31 am

    The new BIG Bore King. Saving a spot in my safe.

  • Jay October 29, 2018, 5:49 am

    I knew this was coming just wasn’t sure when! I use the 450 Bushmaster for the same reasons, it’s a stopper for anything walking this planet of ours. Nice Job Big Horn Armory!

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