Steyr’s ACR: The ’80s-Era Teutonic Wonderwaffe You Haven’t Heard Of

Quick: What’s the most advanced infantry rifle that was ever designed, but never got the chance it deserved? I’m thinking about a futuristic weapon from Central Europe that fired advanced, lightweight ammunition and featured a high rate of fire “hyperburst” firing mode. Care to take a guess?

Did you say “Heckler & Koch G11”? Well, that’s one possible answer, but another is the Austrian Steyr ACR, an advanced concept designed to compete against the G11 for the American Advanced Combat Rifle trials of the late 1980s. The Steyr ACR was just as ambitious as the G11: It used a separate rising chamber driven by an annular piston wrapped around the barrel, feeding incredibly lightweight polymer-cased telescoped flechette-firing ammunition from translucent polymer box magazines holding 24 rounds.


The Steyr-Mannlicher ACR rifle in the hands of a US Army soldier during the ACR program. Note small details like the adjustments on the futuristic optical sight, the in-line back up iron sights, and the compensating ports on the flash hider. Image source: The Black Rifle II, by Christopher Bartocci


The Steyr ACR incorporated many small details that made it every bit a match for its ambitious German competitor. Instead of the familiar centerfire primer, the ACR used an annular primer ignited when the rising chamber reached its zenith in the action; this simplified the rifle’s mechanism and also improved in theory the consistency of ignition.

Unlike the G11, the Steyr was production optimized with a simple mechanism and inexpensive polymer housing; estimates at the time put the cost of Steyr ACRs at up to $400 less per unit than the existing M16A2. The ammunition, too, was cheaper; 60% less expensive than existing brass-cased M855, while being only 42% as heavy.


The Steyr ACR’s 5.56x45mm plastic cased flechette round, far left. It fired a 9.85 grain/0.638 gram flechette at 4,600 ft/s (1,400 m/s).


Ultimately, despite its promise, the Steyr ACR proved to be a dead end. The ACR trials it was created for did not result in a procurement program, and all rifles tested remained as prototypes only.

Today, you can still see the Steyr ACR, along with the other ACR entrants, at the National Infantry Museum in Ft. Benning, Georgia.

Nathaniel F

Nathaniel is a history enthusiast and firearms hobbyist whose primary interest lies in military small arms technological developments beginning with the smokeless powder era. In addition to contributing to The Firearm Blog, he runs 196,800 Revolutions Per Minute, a blog devoted to modern small arms design and theory. He is also the author of the original web serial Heartblood, which is being updated and edited regularly. He can be reached via email at


  • Martin Grønsdal

    (…) a new service rifle by 1996 😉

    • McThag

      In my Twilight: 2000 campaign run in 1992 or so, there was a limited availability of the G11 as the XM27 ACR and duplex ammo was available for the M16A2.

      As I see it, combining alt histories is more fun!

      • randomswede

        Twilight 2000 is almost more fun these days as some kind of retro gaming, f-ak that sounds like hipster talk.

        • El Duderino

          “I liked it before it separated from our timeline”

      • El Duderino

        Lol that was a fun game. Loved all the equipment books, the art was pretty good for the era. Though, with my friends, once Shadowrun came out that’s pretty much all we played besides the odd AD&D or Gamma World campaign.

        Now, though, with 6+ years of military experience I’d sure appreciate T2K a lot more than when I was 15.

    • Kivaari

      The M4

  • Giolli Joker

    We’ve heard of it…
    What’s up with the titles lately?

    Anyway, an article on the AMR/IWS2000 would be cool as well.

    • asdffdsa

      >What’s up with the titles lately?

      Everything dies eventually. This is just TFB dying from slowly turning into clickbait.

    • Cymond

      At least this time it’s a single italicized word for emphasis, not the usual crazy capitalization.

    • Stonia

      I’d just be happy if the newsletter pop up for every article went away. I’m already subscribed, stop asking.

    • Kivaari

      Not many have.

    • Darren Hruska

      Askoriya AMR, I’m assuming?

      • Giolli Joker


        • Darren Hruska

          Ah, I thought you meant BOTH the Askoriya AMR and the Steyr IWS 2000, both of which are flechette-based anti-materiel rifles.

          • Giolli Joker

            Well, that wouldn’t hurt either. 😉

      • Max Popenker

        well, as far as I know it never existed “in the flesh”, or, at least, in the metal.
        AMR-2000, at least, did exist in several prototypes

  • iksnilol

    Why wasn’t it adoptet? It was cheaper in all the ways.

    • Giolli Joker

      AFAIK, wounding capabilities of tiny flechettes were not so good nor consistent, so was accuracy and sabots could hurt friendly forces close to the shooter.

      • ostiariusalpha

        The sabots had inconsistent detachment from the flechettes, which hurt precision of shot placement, but this was considered a minor impediment that could be overcome with tighter fabrication control.

        • randomswede

          I’m not sure they could fix the wounding characteristics however.
          I imagine the flechette would have to fold on itself lengthwise or splinter and arc to cause a large number of small bleedings.

          • ostiariusalpha

            The flechettes tumbled nicely in testing on ballistics gel, and created good sized wound channels. They had the same weakness to fleet yaw as M855 though, and when they didn’t tumble the wound was tiny. The real problem for the flechettes was penetrating sheet metal and glass, they’d poke through easy enough, but you wouldn’t know where there trajectory would be going after that.

          • randomswede

            The rapid 3 round bursts would have mitigated that somewhat but it’s not an ideal solution.

            The approach they took to flechettes appears to have been: “If 5.56 is better than 7.62 then 1.6 must be even more better”.

            Perhaps a 3mm flechette could work; even without exotic materials.
            More recoil of course but that’s why they make you do push ups.

          • Kivaari

            That is not what Fackler’s team found. The “terrible wounds” caused by flechettes were observed with artillery delivered dart. Hitting intermediary objects caused the wounds that were mistaken for being from undamaged flechettes.

          • Arathar

            No, thats crap. Clean shots into test mediums was made and filmed in slow motion.

            It just not always had a 100% chance to bend when it hits. Which is extremly easy to fix, with better designs.

          • Kivaari

            I am going from the letter he sent me, along with his letter to Army Times.

          • Arathar

            Yes they did not always bend reliable. But “fleet yaw” ? Its fin stabilized and flys completly straight, but bullets with spin stabilisation are like a slowed down Top in air. If they hit at an angle they tumble in flesh. If shoot from a 1:7 barrel (meant for tracers) and M4 carbine (not as fast) they have a higher chance to icepick.

          • ostiariusalpha

            I don’t know if you’ve been keeping up with the discussion on this blog regarding fleet yaw, but it occurs at a relatively short distance till the projectile reaches full stabilization. This rear bobbling action happens both in spinning bullets and fin stabilized flechettes. If the flechette does not suffer a fleet yaw error, then they tumble and buckle quite reliably after penetration of the target. Also, a spinning bullet the hits straight on will still tumble it it is a spitzer.

    • The program required a “100% improvement over the M16A2” with “double the hit probability.” While the ACR is absolutely awesome, realistically there is no firearm that will offer a “100% improvement” over the M16A2 without some sort of integrated ‘Smart Optic.’

  • Tony Williams

    If the cylindrical telescoped LSAT/CTS ammunition is ever adopted, Steyr might well want to pull this one out of its museum and see if the basic design can be adapted to use the ammo. The centerfire primer would add a complication but apart from that it would seem an interesting prospect.

    • MPWS

      Ideas may converge in some unusual way and I have to say my thought in past were similar. One way of potential development direction would be to experiment with different projectile diameter. If it reached a size of realistically sized bore, say 3-4mm it may not require sabot. At that point it would also have better ballistics, namely due to excellent section density and better wounding potential.

      One reservation I have with this design is that due to its operating concept (basically a slam-fire) it may not be entirely safe, as some above testimony indicates. Also, fouling is imminent and chamber area has poor access for maintenance.

      • Steyr was convinced that the ring primer polymer case couldn’t handle the pressure curve involved with a heavier projectile. Depending upon the weight of the projectile, the case would need either metal reinforcement or an entirely metallic case.

        • Tony Williams

          But if it used the LSAT/CTS ammo it wouldn’t have a ring primer, as those are centerfire rounds.

          • True, but my comment was aimed at MPWS’ idea of upbulleting the Steyr ACR cartridge.

          • ostiariusalpha

            Right, it’s similar to the limitations that rimfire ammunition has.

      • Arathar

        No such thick Flechettes have no advantages at all. I could writhe a page of text why this idea is terrible, but that would cost me too much time, overall its: Extrem chamber pressures (tiny bore with too heavy projectile), too much contact to the barrel, less bc than a well designed high end Flechette, Far less penetration, much worse trajectory and speed. Too heavy rounds.

  • kregano

    I have, in fact, heard of it a LONG time ago.

  • Joe

    Could the operating mechanism be adapted to use traditional cartridges?
    Looks to have a shorter LOP than most bullpups, which piques my interest.

  • Ranger Rick

    Nathaniel, this is not as obscure as you might think. This testing program was a big deal at the time.

    • Ron

      I remember watching a piece done on the testing on one of the morning shows either in the late 80s or early 90s.

  • Wolfgar

    The Steyer’s firing mechanism was over complex. The entire chamber moved rather than just the bolt. The flechette’s sabot proved hazardous to the shooter and fellow soldiers. After the mechanism failed and injuring the test shooter it was dropped. I’ll pass on this one.

    • Kivaari

      If the simpler chamber moved, instead of a more complex bolt, that may not be a bad thing. It doesn’t hurt to be simple, if it works.

    • Arathar

      It actually was one of the most simple designs ever made… . Insanly simple trigger, a simple non recoiling vertically moving chamber (instead of a big standart bolt moving forward and backwards and trow you off target). And its one of the simplest Firing pins ever, (instead of all that hammer mechanism bullshit in a rifle) it just was fixed in one place and poked the polymer case.

  • My platoon and I all got the chance to fire the Steyr ACR, along with some of of the other rifles the Army was considering… including a Colt M-16 that had a tall Shotgun Rib and fired Duplex ammunition. The Steyr ACR was very light in recoil firing singles and the burst felt more like a normal rifle. Super flat trajectory, but accuracy was not all that impressive. It jammed like a jazz band too. Probably because it had become quite filthy. None of us really cared for it.

    • Dracon1201

      How was the tall rib M16? I was quite interested in that project, it was pretty cool.

      • Kicked pretty hard due to the heavier bullet. But not bad. Not accurate though. The second bullet wandered randomly.

      • Phil

        Rib was up to current sight line, about 1.5″ above bore. The cool thing was an integral suppressor on the barrel which kept blast and rise down. I have samples of the ammo somewhere as I go to demo it for Colt at several ADPA meetings and at Aberdeen. It was pretty accurate with ball ammo and the guy below is right the duplex was way gone pretty shortly after launch, maybe 50-75 yards, of course if your hold was “random” you had a chance of a hit!?! I found the recoil was significantly less in the full on version with the suppressor but perhaps George didn’t get to fire that one. The optic was an improvement for longer range and that was about the only thing that came out of the ACR program. All the guns were failures to some degree for a military weapon but they also saw everyone shoot better when they could see. Shock, that finally penetrated the staff some 10-15 years later. It was a fun program and Ullrick Zedrosser who designed the Steyr was a superb gentleman and amazing guy to talk with on firearms design. As noted elsewhere the flechette rounds were found to be essentially ineffective on humans when launched from a rifle. They worked okay out of artillery but the blast to spread them also deformed them which lent to their efficacy on impact, especially combined with there were hundreds from a shell not one at a time from a rifle.

    • ozzallos .

      But it never got the chance it deserved!

      • Kivaari

        The flechette rounds were shown to be very ineffective.

    • ostiariusalpha

      The breech sealing flap of the newer LSAT polymer case probably would have helped a lot in keeping the action cleaner.

    • gunsandrockets

      How was the muzzle blast?

      • Minimal from the shooter’s perspective.

        • gunsandrockets

          I’m surprised.

    • “Jammed like a jazz band” is my new favorite shooting aphorism.

      • My new pistol has many charms,
        But it has more jams than Hickory Farms.
        Inscribed on the slide is the motto
        “Single-Shot, Semi-Auto,”
        And rapid fire doth tire my arms.

        – Mitch Ota

        • Lonnie

          sounds like a S&W Model 39 I had many years ago.

  • Dracon1201

    Didn’t it burn out barrels too fast as well? I thought I heard that. Hmmm. Well, if they had just simplified the firing mechanism this might have worked.

    I want one of those high rib m16s, though.

    • ostiariusalpha

      No, the sabots were actually easier on the barrel than a normal copper jacketed bullet.

      • Dracon1201

        Sweet, must have been another proto I was thinking of.

        • ostiariusalpha

          I believe that was more a problem for the Colt duplex ammo; two bullets down the barrel is twice the friction.

        • The guts of the G11 are easily the most complex thing I’ve ever seen stuffed into a firearm; the mechanism looks like something designed by a company that was paid by the part, it must have been a nightmare to keep clean.

    • randomswede

      If my memory serves me it was the very high chamber pressures that where the main concern for life length.

  • roguetechie


    Personally I was much more impressed by the AIWS Gene Stoner worked on. I have always wanted to see an AIWS in 5.56 FABRL. That would be one sweet and handy little weapon!

    Between the 90 round belt drum, dead simple plastic belt, and the FABRL’s. blistering speed and light weight it would have been a genuine apex point in the SCHV concept. Especially when you throw in short flight times, light ammunition, and crazy quick flight times to 500 meters. Personally I want to see a round like this or 7.92×41 cetme adopted for military service. I believe that they would prove to be winners.

    • Here’s a few photos of the Ares AIWS prototype.

      • gunsandrockets

        What photos?

        • It may be a Disqus issue. They show up fine in two different browsers when the article is accessed via TFB’s website.

          • gunsandrockets

            They are showing up now. Strange.

          • randomswede

            It could be a moderator issue; just to make sure it’s _gun_ porn.

      • TJbrena

        Neat! Here’s a couple AAI brochures for their ACR and CAWS entrants.

        • That is AAI’s first-generation ACR candidate, back when the US Army was only funding caseless research.

          • Here is a composite photo of the final ACR candidates.

          • iksnilol

            what was the last one in the picture?

          • That is the 2nd Generation AAI ACR. This variant fired a saboted flechette loaded in a standard 5.56x45mm case. However, it was not safe to use with conventional 5.56mm NATO ammunition.

      • Maaannn, if we’d put these into production we wouldn’t have lost the Cylon War!

      • roguetechie

        Thanks Daniel, I have a copy of black rifle 2 and I absolutely love this gun.

        Another gun that should have been is the XM248. that gun was absolutely amazing in every way, especially where you realize the gun with loaded 200 round box, sling, spare parts and tool roll, and a full length barrel weighed less than current short barrel m249’s do with no ammo, no feed bracket or t&e, and zero accessories?

        They also had a 7.62 NATO conversion kit in the works which even fully loaded and with the same stuff from above list also weigh less than that stripped down 249 with no ammunition, or even a way to hold the damn ammo if you had it!

        In about a decade back then we had a chance to get the SAW, M73/219/85, and a revolutionary M2 replacement we could have had… All of these caused by either inept or downright corrupt decision making. Oh and not only were these guns lighter than the guns we have now, they were also CHEAPER! We’re not talking a little cheaper either.

        On a hilarious note the 248 fully equipped with the items listed earlier was a whole 2 pounds heavier than the LSAT LMG is projected to be.

        • The Brigadier

          Do you have any pictures of the XM248? I followed a thread in another forum about this rifle and everyone waxed rhapsodic about it there also. I would like to know more about it.

  • Mick Finn

    The best Rainbow 6: Rogue Spear weapons mods had the G11 and the ACR. I base most of my obscure weapons knowledge on the game. I’m not even that embarrassed.

    • Good times…

    • Lonnie

      most of us live in reality, not in a video game…js

  • I find the range more interesting in the video than the guns since I pretty much knew about them. The detection mechanism for the spot placement was interesting. Using the curved steel structures to sense the shock wave is a method I had not heard about. From my understanding they use to microphones these days to determine shot location for a round passing over them.

  • smartacus

    loox like an 80’s era “body bike” style motorcycle

  • randomswede

    I had heard of it, I want my money back!

    I’d appreciate an in depth article on the SPIW however that thing is just the bee’s knees.

    • I’ve only seen one good write-up of the Ares FARC in a mid-1980s Harris Publications annual. I’ll have to dig it out my boxes.

      Blake Stevens did a three part series on the SPIW for Small Arms Review recently. It was mostly a condensed version of his book “The SPIW – The Deadliest Weapon That Never Was.”

      Several SPIW test documents can be accessed online via the Small Arms Review archives and One of the best sources for pre-1968 SPIW history can be found in one of the appendices for the “Report of the M16 Rifle Review Panel,” which focused on the Army Small Arms Program.

      • randomswede

        Is this the top of that Harris write-up?
        In a hasty google spree that picture and a list of the rifles basic features was all I could find.

        From that; it sounds like the AR-15/AK/VZ-58 amalgam/alloy, with some fresh sprinkles on top, that we have been evolving towards.
        Some of the sprinkles probably needs to “stay in the box” while others could be golden.

        Also, thank you for the leads on SPIW information, it’s my favorite kind of “madness”.

        • Yes, it looks like it. I want to say it was either their 1983 or 1984 “Assault Weapons” special. The article was written by Gary Paul Johnston.

          • randomswede

            If you you do dig it up, I’d love to partake.

  • Marshall Price

    I remember seeing these at the museum at Ft. Benning just after I graduated OSUT. Future weapons of the past. Way cool.

  • Kivaari

    Around 1989 Dr. Martin Fackler sent me a letter and a copy of an Army Times op-ed he had written saying the concept of flechette rounds was totally flawed. He and his staff were arguing with the staff at Picatinny Arsenal regard the ongoing studies regarding this rifle and ammunition. Fackler hated the flechette, as being a very poor killing device. The “needle” that self-corrected any tendency to tumble, simply id not leave adequate wounds. I’d agree.
    This rifle WAS interesting. The cartridge, had it used a real bullet, is simply a great idea.

    • ostiariusalpha

      Fackler… was not always as dependable a source for terminal ballistics as you would hope, I’ll put it that way. The Picatinny Arsenal guys argued with him because the knew he was full of crap on this subject, as he was on many things. At less than 900 m/s, a flechette will simply punch a straight, tiny hole in ballistics gel with a minimal permanent wound channel; on harder materials, it will often simply fail to penetrate at all. But, at above 900 m/s, it destabilizes rapidly and buckles as it tumbles, creating progressively more severe permanent wound channels as the velocity increases. The Steyr ACR flechettes had a muzzle velocity of around 1500 m/s, and could create tissue destruction and bone fragmentation as devastating as anything the M193 round was capable of. This is all well documented stuff that can be looked up on the DTIC site.

  • Diamondback

    Looks like a prototype of the Hi-Point 995TS 9mm Carbine.

  • Tassiebush

    Haha I love the claim in that video of the first percussion firearm being the Mississippi rifle! Rev Forsyth would not be pleased!

  • Yeah, that is the one.

  • Padmmegh Ambrela

    Difference between Flechette round vs Sabot Light Armour Penetrator (SLAP) round?????

    • Arathar

      Flechette: Far Cheaper, more aerodynamic, better barrier penetration compared to cost.

      Slap advantages: made out of tungstencarbide …which also could be used for Flechettes…
      There even is Cylindrical polymer cased APDSFS (basicly Flechette) ammo for 40mm barrels. And fired from a genius G11 rotating chamber action.

  • Too bad the only advantages it really had over conventional assault rifles then available OTS were entirely due to Steyr using absolutely ineffective ammo.

    Flechettes, other than in large groups (such as used by artillery), suck.

    • Arathar

      Are you kidding me? The main weight of a round is the projectile.
      Low recoil due to KE=1/2m x c²
      Insanly flat trajectory! Unbelievable penetration of Cover and Armor. Short fly time.
      Bend instantly in Flesh, (i dont want to be hit one with almost 5000fps)
      The main problems: Inaccuracy, and not enough energy.
      Solution: Better manufacturing process, bigger and longer Flechettes with 2000Joule. Instead of 3 small at a unnessessary 2200rpm 3 round burst.

      (Burst only makes sence at around 1200-1600rpm, a person running sideways to you (from cover to cover) runs to slow to give 2200rpm any better % of hit)

      I actually work on Flechettes, it took a shitton of time (2years), but now got high end designs, that outperform anything, and still are extremly cheap.

      • In actual testing, the Steyr ACR flechettes sucked at both penetration and wound channels, compared to conventional bullets.

        Poking tiny holes in tissue and shattering on light steel armor plate the “obsolete” bullets go through means your low recoil and flat trajectory is useless, militarily.

        I have yet to see any credible reports of effective small arms flechettes, despite reading decades of scientific literature and formal, professional test reports on them in the last twenty or so years I’ve been reviewing ballistics reports.

  • Daisuke0222

    So… does the problem that the ACR program was supposed to solve (doubling hit probability at 300m under combat conditions) still exist, or have modern optics on an otherwise conventional combat rifle helped to improve that?