HK51: The SAS’ Full Auto Flashbang Dispenser

The HK51 is not a gun that was ever actually produced by Heckler & Koch. It is instead a variation on the G3/HK91 originally developed by American H&K specialist Bill Fleming. He was contracted by a UK-based company called FR Ordnance to produce a submachine gun sized version of the G3 for British SAS and SBS use. Both agencies did actually buy a few examples, and used them a few times operationally. Some testing was done on specialty ammunition for them, but they were ultimately replaced by the rather more practical HK53 (essentially the same gun but in 5.56mm).

Where the HK51 saw most of its sales was on the US recreational market, with both Fleming and others making the guns, often in combination with registered H&K auto sears. With full-power 7.62mm NATO ammunition and all of an 8.3 inch barrel, the HK51 serves best as an attention-getter on a range full of other machine guns…


  1. I never like being critical of a firearm, but this video has opened the door. I have NEVER liked this shortened version of an HK styled weapon especially in this caliber. The HK53 makes infinite more sense over the 7.62×51. A 7.62×39 would have also made much more sense for this weapon. But I can see as the UK does not utilize the CommBlock round, for the SAS to go with the HK51 makes a little more sense. That round would be in their logistics line, especially in the field. But how hard is it to secure the 7.62×39 round almost anywhere in the world? Plus, the PTR version of this super short rifle has had some bad reviews, with it exhibiting too much bolt velocity, thereby leading to dimpled receivers. It definitely is a “flash bang” firearm. Nice review. A 13″ barrel seems to be the shortest length the caliber should practically be applied to, for several reasons. Thank you as always.

  2. I’ve shot a 53; once. Yes.

    Big fat fail compared to the aksu; a wonderful contraption. Not praising Osama but Osama picked the best gun.

    Fantastic contraption.


    • I have always thaught taht an HK53 in .300 Blackout would be quite the practical gun for the MP5 sized gun role with more power than 9×19. 5,56 out of the HK53’s 211 mm barrel is not exactly comfortable either. The .300 Blackout shoudl have burnt most of the powder in the barrel makng less flash and bang than 556.

  3. Having run quit alot of 7.62 NATO through a G3 in full auto (fun, but not super easy to control) I can’t imagine this short version being anything enjoyable to shoot. But yes, it sure does look cool!!!

  4. Besides being “the latest shiny thing to chase”, why would the British want it? Try as I can, I can’t figure out the tactical niche this thing was supposed to fit into. Maybe a decoy to distract everyone’s attention, while the assault team moves in? It seems a perfect illustration of “Just because you can, doesn’t mean you should”

    • Yeah, it sounds like “keeping up with the Joneses just because you can.” Here’s my two-bits from the civilian peanut gallery: DO NOT WASTE OUR TAX-PAYER MONEY ON KEEPING UP WITH THE JONESES.

      • The Sterling Mk VII (aka L2A7) was specifically developed as a suppressed version of the Sterling to supplement the suppressed Sterling L34A1 (Mk V). The difference was that the Mk VII could be broken down into two parts, the gun and the suppressor, for covert carry concealment.

        The L34A1, by comparison, has a fixed suppressor which only an armorer is supposed to remove and break down for maintenance. At roughly one meter long with the stock folded, it’s about as “concealable” as a moose in your fridge.

        Like the L34A1, the Mk VII was only supposed to be used with subsonic ammunition and on semi-automatic. which is the reason the “para pistol” version is semi-auto only, other than legal considerations.



      • 100-120 mm for 9×19 is sufficiently widespread even in “long” (or at least “shoulder”) arms. MP5k, Micro-UZI, TMP/MP9 etc, that Sterling is not that unusual. Not to mention probably 98% of military pistols in 9×19 having a barrel shorter than that.

        But this monstrosity definitely stands apart. I think platforms for full-powered rifle rounds in widespread adoption start about 16″ long… and this is almost half as short.

    • It does have a niche role to fill Colonel. If one is shooting through ones own windshield and into an another vehicle, said vehicle possibly being armored and possibly carrying nasty folks armed with things that go boom, you may feel the need for a compact 7.62 NATO weapon. And it looks fucking awesome.

      • If you had the thing locked into a ball mount, like on an armored car or an IFV…? Maybe you could hold the bastard on target. Maybe. The one I’ve seen fired exhibited what we could, with delightful understatement, term “excessive muzzle rise”. I think that you’d be lucky if you were shooting at the moon by about the second round…

        Every one of Ian’s objections to the G3/HK91 that he addressed in his own Spuhr-updated version a little while ago goes for the HK51, only about freakin’ cubed. I wouldn’t be a bit surprised if the venturi effect from the muzzle device added more to the whole thing than the actual internal ballistics from the projectile, TBH. That sucker looks really, really bad, fired in daylight.

        Coulda been the ammo, though. I dunno; I think this might serve a purpose for handing off to a point man and telling him to use it in case he needs to break contact with some unpleasant heavily-armed strangers. A magazine from this thing on full auto should have about the same psychological effect as having someone set a Claymore off in your face, albeit with highly questionable lethality. I think you’d probably put more rounds into the canopy of whatever jungle you were roaming through than you would in the people you were aiming at.

        Helluva conversation piece, though…

        • I have shot one in full auto, if you like i can post a video of me doing a mag dump, and a drum dump all on target.

    • Covert care in Northern Ireland get stopped at a terrorist checkpoint you empty this towards them & drive away at high speed. Job-Jobbed! Back to the factory for Tea & Medals.

      • I could stand to be corrected, but I don’t think that Doppeltrommel fit into a standard G3 mag well. If I remember my HK MG details correctly, that drum magazine setup required an adapter that replaced the regular beltfeed, which didn’t allow for putting one of the regular G3 magazines in place. I don’t have the references for that, any more, sooo… Anyone else?

        • There is also a single drum made by H&K, that fits the normal G3 style magazine well. It is used to feed the G8 (HK11) in the turrets of the Sonderwagen 4 (SW4; police armoured car) and other such applications. The beltfeed for the G8 fits into the tight turrets as well, but the drum magazine is said to be more reliable. And I guess belted ammunition is normally not in the supply chain of the various states and federal police forces.

          There is also the beltless 100 round feed, that requires a different adapter for the G8. Normally the G8 comes in a sheet metal crate with a magazie well, a belt feed and the adapter for the beltless feed. Though I do not know if the police fores have baught the 100 round beltless feed box.

          Sonderwagen 4:

    • There was also a belt fed version of these offered, for the extra, extra special forces apparently. RIA sold one in their Sept 10th auction, went for $40K and change. I hope Ian got to do a firing video with that one, a 200 rd “belt dump” would be the perfect video ending! Although I suspect most of his facial hair would be burned off by the fireballs long before the belt ran dry. “Am I missing an eyebrow?”

  5. Now I want to see it fired at night. Or better, at late dusk, so we can see Ian in silhouette, rocking back from the kick.

  6. This is a weird device.
    But, apparently, it really has some kind of practical purpose.
    In any case, besides the short ones mentioned, there is also a 5.56 version, made from the M16.
    The funny thing is that (as I heard) this is really an “automatic flashbang”, with a lethal backup function.
    Which is very well suited for RIOT control.
    Allegedly, after a series of such a device over their heads, the patients’ enthusiasm drops sharply to zero.

  7. I’ve got absolutely no idea about the provenance of the thing, but there was one of these hanging around Fort Lewis back in the early 1990s. Coulda been 2/75 Rangers, coulda been 1st SF Group, could have even been one of the loonier members of one of those organizations who’d gotten themselves a Class III license and was out selling full-auto goodness on the side of it all to the local police organizations. Nonetheless, I’ve seen one in the field, fired on semi-auto only because the general-use range at Fort Lewis did not afford you the opportunity to fire anything on fully-automatic.

    The guys that had it out to shoot with were really cagey about specifically whose gun it was, and were somewhat upset that I recognized it at a glance and went up asking questions about it. Which is why I don’t know for sure if it was someone’s dealer’s sample or it was an SF/Ranger side purchase that they were taking out to play with over a four-day weekend.

    I wish to hell I’d have been able to see it fired full-auto; the guys shooting it were telling me it was about like having a hand-held Claymore mine go off in your face, and that aiming it was… Questionable. Semi-auto was amazing, especially with the German ammo they were firing. The scale of the muzzle-blast was about like one of the 16″ guns on one of the battleships–Fully visible in broad (PNW heavy overcast, mind you…) daylight, and I swear to God, the fireball was about 6-8 feet in diameter. Doubled-up earplugs were a necessity even five bays down from those guys, and that was what drew my attention to them in the first damn place. I thought that whatever they were shooting had blown up…

    I still want to see one fired full-auto. From a distance, and not from the muzzle-end, either.

    • I would bet on the foreign weapons collections of either Rangers or Special Forces as to where the HK51 came from, that you have seen. OTOH, why were they so evasive as to where it came from then?

      • I’ve got no idea why they were so “Go away, kid…” about the whole thing. The interesting thing about the guys shooting it was that they were all very obviously more senior to me, as a mid-rank NCO, and they were not the usual guys from the SF and Ranger units I was used to seeing on the “civilian” range there at Fort Lewis. Those guys were generally my age or younger, and were extreme examples of “gun enthusiast” the way I was; they’d show off whatever they had, usually, on the theory that if they shared their toys, you’d let them play with yours. Not that I had anything really noteworthy, either. Although, at the time, I did have one of the early production ACOG scopes that everyone was lusting over, and which hadn’t yet made their way out for mass issue…

        I’m still unsure what was going on with that whole deal. All I know for sure is that I saw the HK51 being fired on a weekend at the range we were allowed to use on the weekends, and that the people doing it were pretty ‘effing evasive about the thing and where it came from. My best guess is that they were kinda-sorta not supposed to be out there with it…? Maybe because it was a part of the reference collection at the SF group, or they were “borrowing” it from one of the Class III dealers in the unit that I knew about? Totally unknown. It might just have been that whole “Hooah-er than thou” thing you get from some SF and Ranger types; they don’t like mixing with the lower orders of line troops. I didn’t know any of those guys, so I’m not even sure which element they were from–Ranger or SF, because Fort Lewis had both. I’m presuming they were more likely SF, because at the time, the Rangers were notable for conforming to the “high-and-tight” hair style, while the SF guys were generally a bit less “kempt”, which was what these guys were. Not long-haired as though they were “on mission”, but more like “blend in with general population of Fort Lewis”.

        So, honestly, my best guess about the reticence is probably about as good as yours. I never saw those guys around the range before that, and never again after that, although they were suspiciously familiar with the guy who ran the place…

  8. If the story is true that it was made to fulfill a special forces requirement, it shows that emotions like “attention getter” and “it looks fucking awesome” play a big role in special forces decisions on small arms.
    If anybody tries Bionic’s proposal of firing bursts (7.62 NATO from 8 inch barrel!!!) through the own windshield, everybody in that car will be deaf afterwards. And due to the ridiculously short barrel, serious target effect will virtually be non-existent.
    I am afraid the “HK 51” tells us more about special forces than we want to know.

    • “…ridiculously short barrel, serious target effect will virtually be non-existent…”(C)

      Do You, pardon, invent nonsense yourself, or have You read it somewhere? 😉

      Is 2010 fps at 150 gr. bullet is “non-existent”?
      Perhaps You are giving us a favor, catch one with Your teeth? LOL

  9. Didn’t the Australian SAS run cut down SLRs with full auto in Vietnam? Perhaps that’s where the UK SAS picked up the idea?

    • That’s correct. I managed to get hold of one while in VN back in the day. Never actually fired it though. You can find plenty of info by Googling ‘the bitch rifle’.

    • Australian SAS armourers re-barrelled a small number of L1A1 receivers with M60 barrels and also added 30 round BREN 7.62×51 magazines to assist in sustained fire suppression. Some of the barrels had modified flash suppressors while others had the M60 flash suppressor. These conversions were used by the SAS for special operations using Iroquois helicopter insertions in jungle terrain during the Australian involvement in Vietnam. The reason for this was for close range suppressive fire where the M60 GPMG were found to be too unwieldy for SAS special operations. There are very few in existence. The Australian War Memorial has one not currently on display and another one is allegedly in the Singleton Small Arms Museum.

      • The example that I had was an L2A1 receiver with the L2A1 barrel cut back to about where the original gas port would have been. The gas cylinder and handguard was cut back by a similar amount. Magazine was 30-round L2A1 type. There was no flash suppressor and no front sight either. Would have been interesting to fire. Also, I encountered a ‘field modified’ M16 which had about 4 inches of barrel, no gas tube, and no butt or return spring/tube. US MPs had it. Was manually loaded, using the magazine and cocking handle. Sort of like a broomhandle Mauser layout. I did fire it – noise, blast, flash and shock effect on my face was staggering!

        • “…a ‘field modified’ M16 which had about 4 inches of barrel, no gas tube, and no butt or return spring/tube…”(С)

          I was talking about something like this.
          Only the barrel (probably) was even shorter. Cut off so that you can see the bullet.

  10. I am deeply deeply sceptical about the alleged British SF connection. By 1990 they were already using the 53 (a bit, though had seen its limitations) and the G3K.

    Maybe they bought or were given one or two for trials (aka “a laugh”). But I just don’t buy the idea that the People We Don’t Talk About would buy an American comedy Hollywood gun for serious use.


    • Where in the UK are you going to go, if you want something like this? It’s not like there’s an actual small arms industry, or anything. Fleming and Vollmer were well-known internationally for doing the things that HK wouldn’t, so if the SAS or others wanted something to experiment with, I could easily see them going to either one.

      I remember seeing stuff about the HK51 in the press back during the mid-1980s, which was why I recognized what the guys were shooting that day I describe up above.

      One of the issues with them having done this with the SLR is twofold; one, no full-auto capability built-in, and two, best you’re going to do is shorten the gun to the length of the gas system. With the recoil-operated system of the G3, it’s a hell of a lot easier to get those short barrels.

      Insanely enough, there’s also a Fleming-produced ad out there for an HK52K, with an MP5K-style foregrip and no buttstock. 4.7″ barrel. No idea about that one, at all, but I think it would be of even less real utility than the basic HK51.

      There’s a lot of “Hey, we’ve got the money… Let’s try it!!” mentality over in the SF community, world-wide. There’s also a lot less supervision from the official parties, so they can get away with murder, compared to other sorts of soldiers.

      I rather doubt Fleming or Vollmer would have put the work into these things, unless they thought they had a market which would actually pay for them. Somebody was actually buying these things, and in enough quantities to justify doing all the work to make them happen.

      As to who the hell that was? I’ve never seen any documentation, but I’m pretty sure that Ian has, or he wouldn’t be saying anything. It’d be nice if he could share it…

      • I’m guessing, and this is just a guess, that this beast came along after the failure of this one;

        From the Wikia;

        The Sterling 7.62 was a battle rifle/light machine gun variant of the Sterling submachine gun which was manufactured in the 7.62×51mm NATO calibre. It used lever-delayed blowback to handle the more powerful rounds and was fed from 30 round Bren magazines as well as 20 round magazines from L1A1 SLRs. A bipod and detachable fixed stock could be added as well as a Single Point IR/Trilux night sight. To prevent ammunition cook-off, the weapon fired from an open bolt. As the Besal was a planned LMG of World War II, the 7.62mm NATO calibre Sterling was intended as an emergency standby weapon in case of attack during the Cold War.

        In his article, Ian points out that the gun uses the FAL 30-round magazine, also normally used in the L4A1 Bren.

        My best guess is that it was intended to serve as the SAW for an SAS/SBS unit, substituting for an L4A1.

        The HK51 would seem to be a more reasonable (or less unreasonable) alternative to the L4A1 where compactness might be a consideration.

        Since it would likely be used at ranges under 100 meters, the short barrel would not be enough of a handicap to velocity to worry about.

        And if you want to suppress an enemy small unit long enough to evade, a 7.62 x 51mm firing full-automatic would likely do it be scaring the bejebus out of them, especially at night. “Flashbang” indeed.

        BTW, there was in fact a 7.62 x 39 version of the HK91/G3 series, the little-known HK32. It was apparently intended to be sold to African countries where 7.62 x 39 ammunition and AK rifles were abundant. There seem to have been no takers for it or its near-twin, the 7.62 x 39mm Rheinmetall RH4.

        Either one might have made a more reasonable “ersatz Bren” for SAS/SBS, but of course 7.62 x 51 was in their supply chain and 7.62 x 39 generally was not.

        As I said, this is mostly guesswork, take it for what it’s worth.



  11. Bionic Commando is right.

    One of the numerous S.A.S memoirs (I think “Andy McNab”‘s second book) mentions this. There were a limited number procured for use against the IRA in NI. As Bionic Commando says, the IRA was increasingly using vehicles, including some with improvised armour. The MP5 and HK53 were not quite up to the job when firing into cars. Even unarmoured ones. Windshield glass in particular would make 9mm shed jackets and disintegrate, causing only superficial frag wounds. This was particularly the case when firing out of your own vehicle into theirs. What was wanted was a HK SMG sized weapon that could be carried in the same places as an MP5 or ’53 (under a coat, in a gym bag, in the door pocket of a car etc), but that would have the power required to penetrate vehicles better than 9mm/5.56.

    The book says that initially captured folding stock Argentinian Para FALs were used until the ’51 was procured.

    I have also found a reference to its use by 14 Intelligence Company, for exactly the same purpose. There is a memoir by one of them, (“James Rennie” / The Operators). A book I highly recommend BTW, all about the plain clothes operations against the IRA with some very interesting details on training and methods.

    I should also point out that just because a weapon is capable of full-auto, doesn’t mean that you have to, or should use it that way. It is quite likely that the British SF users rarely used it full auto, particularly in the close proximity of innocent bystander, as would be the case in NI. IIRC, McNab also mentions wearing safety goggles and hearing protection with built in radio speakers in these plain clothes vehicle operations when things went kinetic.

  12. I have significant experience with the H51, and as everyone has already mentioned it has its limitations, and slinging 7.62 NATO in full auto has no practical use other than suppressive fire, but I will say from experience that when selected to 3-round burst, a proficient shooter can be very effective with the 51, and it’s size does provide some advantages if you’re spending significant amounts of time in a vehicle. Our training produced consistent effective burst fire up to 300 meters (granted our proficiency with the weapon was above average), and in CQB selected to single-shot (or burst) was quite effective at defeating body armor as well as penetrating positions of cover. Even if stopped by a vest/plate it is going to knock them down and expose them to a finishing round, not always a guarantee with 5.56. I do agree that 7.62×39 would have been an outstanding alternative for weight, though from a ballistics standpoint I personally would still take 7.62 NATO in a fight. Every weapon has its limitations, but I would not underestimate the 51.

  13. I had the dubious pleasure of seeing a belt-fed version fired at Knob Creek a number of years ago. It produced a man-sized orb of fire at the muzzle, and the muzzle blast felt like a slap to the face even from thirty feet away.

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