Mauser’s high-tech antitank gun: the 2.8cm sPzB 41

An sPzB41 in excellent condition at the Musee des Blindes, France (image source: wikimedia commons)

During WW2, having increased anti-armor capability was of ever-increasing importance as combat operations progressed.  One way of increasing armor penetration was to use the “Squeeze Bore” principal.  This principal was initially explored in German small arms design by Karl Puff in the early 1900s, and further explored by Hermann Gerlich in the 1920s. By reducing the size of the bore smaller than the original diameter of the round as it traveled down the barrel, both sectional density and velocity increased.  The Germans utilized this principal in the Mauser-Werke produced 2.8 cm Schwere Panzerbüchse 41.  Using a breech that would close automatically upon loading, the sPzB 41 had a hydraulic recoil buffer and spring-driven recuperation.  There was no traverse/elevation mechanism; the gun was aimed manually.  Besides the base model issued to Jägers, there were also packable variants with lighter carriages and no shield issued to Fallschirmjäger and Gebirgsjäger troops.  For an even lower profile, the wheels could be removed.

Squeeze bore designs were also utilized in the 4.2cm PaK, and the 7.5cm PaK, which all had tapered bores that would compress a softer outer jacket of the round around a tungsten core.  The sPzB 41 even was able to penetrate certain areas of Soviet heavy tanks such as the JS-1, which was impressive at the time for a 2.8cm gun.  Service lives of the barrels were short due to the stresses of the design, but a service life of 500 rounds was in the ballpark of the combat life of such weapons systems. An eventual tungsten shortage ended their employment in combat, though many of the 2.8cm guns were mounted on 250 and 251 model halftracks.

The British Army, on the other hand, used a bore-reducing muzzle attachment designed by Czech engineer František Janeček on their Daimler armored cars and Tetrarch tanks.  In conjunction with an appropriate “armor piercing super-velocity” round, the Littlejohn adaptor increased muzzle velocities as much as 350fps for a flatter, faster trajectory and more armor penetration capability from a small gun.  The problem with the adaptors was that they precluded the use of all other ammunition and had to be removed in order to employ a HEAT round, for example.

Littlejohn adaptor fited to a barrel (Image source: British ordnance collectors network)

Littlejohn adaptor fited to a barrel (Image source: British ordnance collectors network)

There were a few attempts by the US ordnance board and the Soviets to develop weapons using the squeeze-bore principal, none of which proved successful.  Ultimately, there are many better options out there for antitank capability these days, but perhaps squeeze-bore or cone-bore barrels will come back into fashion someday.

Rusty S.

Having always had a passion for firearms, Rusty S. has had experience in gunsmithing, firearms retail, hunting, competitive shooting, range construction, as an IDPA certified range safety officer and a certified instructor. He has received military, law enforcement, and private training in the use of firearms. He is fortunate enough to have access to class 3 weaponry as well.


  • vwVwwVwv

    from mechanical terms we haven’t moved far from the 1950’s,
    our electronics is beter, our materials mordern, we produce more but it is all based on
    old stuff, evan the space craft we use now is a Sojus from the late 60’s.

    • cs

      Decades of reliability.

      • vwVwwVwv

        …are the only excuse for our pride. 😀

    • tts

      Until the materials and manufacturing methods improve not much will change unfortunately. Materials science and manufacturing are 2 areas which are incredibly slow to change too.

      3D metal printing and nano materials might be getting good enough that they could make a big impact in a decade or so though. Seems like every other month there is some sort of interesting development there. Lets hope it comes to something sooner than I’m expecting! I still want my flying car. Or at least 1 that gets close to 100mpg without looking weird and sitting 1 person.

      • vwVwwVwv

        1920 we had 6 to 12 different locking systems for auto pistols.
        1980-90 with aloy, steel and plastic frames, with…. rotateing, gas pessure,
        blowback driven, walter and browning locks.
        everyone wanted to make
        things beter
        and now? now the man in smokings make the decisions and
        you have glock and 1911 copys with different brandings.
        it hurts a litle bit.

        • Sianmink

          Have you taken your meds today?

          • vwVwwVwv

            no i am just angry about lack of progres, so you need meds daily?
            wish you a fast recovery.

          • Buck Timlin

            You aren’t connecting with his subjektive vive? I know I am.

        • Edeco

          This reminds me of myself before I learned to stop worrying and enjoy the service economy.

          • vwVwwVwv

            good luck. 😉

      • Jake_Barnes

        Remember that SpaceX has been producing rocket engines with 3D printing. I think that 3D printing is coming of age right now.

    • Andrew

      Next Gen space systems like SpaceX’s Dragon capsule, and Falcon rocket, are using the latest production methods to create lighter and stronger components. In fact, the Falcon rocket is now using 3D printed components on the main engines, from pumps to nozzles.
      The scary part of the Soyez system is that it is actually safer overall than that bloated whale of a shuttle that we were stuck with.
      The truly unfortunate thing about the US program is we could have had much superior Apollo capsules, to the extent of 80% reuseability for long duration missions, and an enhanced and enlarged Gemini for low to mid orbit work (Gemini system was very safe and cheaper per astronaut than Apollo.) Both, along with next gen launchers based on Saturn systems (from single F engine launchers to super Saturns with strap-on boosters) and permanently orbited tug systems would have given us a greater space presence than the bloated Shuttle ever did.
      Ah, sorry, this is a gun site, not a rocket site.
      Just wanted to see a NERVA system in operation before I die.

      • vwVwwVwv

        yes there are developments, but it is a bit of, i dont know how to say,
        the efforts are from privat entusiasts rather than from the
        society like in thr 70’s or 80’s. we have
        “won” the cold war and now
        we need no developments. in the 80’s whole universitys worked on
        innovation. it looks like we are sated now and just want to blog and chat
        all day long, the entusiastic flame is now a peace of cole.

        i would like to see komplet new guns, how about a pistol in 500S&W?
        thanks for your coment, it is interesting, i will do reserche.

  • iksnilol

    I remember that Annies usually have a slight squeeze at the end of the barrel. That helps accuracy and is the reason why nobody recommends cutting down an Anschütz.

    Squeezebore 5.56 barrel would be interesting. Squeeze it down to 5 or 4.5mm or something. Should help making the trajectory flatter, even with a shorter barrel.

    • MPWS

      That much of reduction on .223 bullet is not possible, but I recall specs on forged barrels with .001 – .002 reduction at muzzle. That is well doable.

      • iksnilol

        Oh it is possible.

        Wasn’t it P.O. Ackley who shot 8mm bullets through a 6mm bore without issue.

        A reduction of .001-002 at the muzzle is meaningless in regards to ballistics.

        • Ken

          I believe he received a Type 38 Arisaka that someone sent in. Upon inspection, he had found that the guy rechambered it to .30/06, but left the 6.5mm bore. The gun didn’t blow up and the .30 cal slugs swaged down to size.

          In Hatcher’s Notebook, Julian Hatcher reports some boys who got their hands on a Type 99 and some .35 Rem ammo. They managed to hammer the bolt shut and fire two rounds just fine, but the third round blew up the receiver.

          • iksnilol

            Jupp, then he did some testing as well. And found out as long as you have the correct throat so that the case can release the bullet then you should be fine with the barrels swaging down the bullet.

          • Ken

            I can’t confirm because I’ve never seen an example, but I’ve heard rumors that the Austro-Hungarian military rechambered captured Mosins to their 8mm caliber by simply reaming out the chamber. With a gentle throat, these supposed conversions were supposed to work great.

    • Ken

      Just about all barrel bores are a hair smaller at the muzzle than at the breech end. After the blank is drilled, they carefully measure it to to figure out which end is smaller. It’s a very minute difference, but that way is better for accuracy.

      • iksnilol

        True, but the Annies have a tighter muzzle than normal guns that I’ve seen.

        • Ken

          Yeah, they do that intentionally. People do that to muzzleloading match rifles too. I’ve talked to some old timers who say they do it by hand using lead hones with abrasive compounds to taper the barrel.

    • Ben

      The Canadian produced M16 copies (C7) actually are squeeze bore rifles. Doesn’t make a large accuracy difference with military ammunition, I’ve heard.

  • guest

    probably ment IS, and 2 instead of 1.

    The gun itself though being an interesting concept is as obscure and as pointless as that polish AT rifle that did not use any penetrating rounds, but relied on the backside of the armor spalling due to great velocity… same kind of concept the british used post-war but with explosives.

    “Ultimately, there are many better options out there for antitank
    capability these days, but perhaps squeeze-bore or cone-bore barrels
    will come back into fashion someday.”

    No, they won’t, just like curved barrels and black powder.

    • Rusty S.

      Though the series of tanks is referred to as both IS or JS, I meant JS-1. Also known as JS-85. Produced from oct. 43 to Jan. 44. I don’t know of any successful hits on JS-2 tanks.

      • guest

        No. The name of the tank is IS as an abbreviation from the name Joseph Stalin. That the name “Joseph” is spelled “Iosif” in Russian does not mean it can be “reversed back” later on for convinience or some other reason.
        As far as IS-1 goes it was produced in very limited numbers, and any actual German testing was probably conducted on IS-2.

  • vwVwwVwv

    right, thats what i wanted to say, a bit 3D and a drop nano, no on wants
    to make the new, best, strongest…… just no experiments…

    this Burgess thing is awsom, no realy, i am impressd, wow.

  • Jay

    The Germans dropped the squeeze bore idea rathed quick, for two reasons. The shells had more drag and velocity dropped faster than conventional rounds. For example, the 200m/s slower shell shot by the 75mm PAK 40, outperformed the 75mm PAK 41 past 1000 meters. And the second reason is that, squeeze bore AT guns required tungsten penetrators. Tungsten was in short supply in Germany.

  • Alex Kevarsky

    “principal” is something else. You want “principle.”

  • demophilus

    A buddy of mine had been in the Austrian army, and claimed they had some squeeze bore barrels for their AUGs. Not a big taper, but enough to increase muzzle velocity and accuracy a little. He also said that the bullets got more frangible, enough that their JAG corps decided the barrels shouldn’t be general issue. So they ended up issuing them to snipers and CT units.

    Don’t know if it’s true, but it’s interesting. IIRC, the AUG had a quick change barrel back then.