Bonus Video: Lahti L39

I had the chance to shoot a 20mm L39 Lahti antitank rifle (cannon?) at a recent get-together. It is the cheapest of the 20mm guns you can generally find, but also one of the less pleasant to actually shoot. In this case, the gas system was turned off to help preserve the brass, so I got to eat the full force of the recoil. Normally some of it is absorbed by the action cycling. Notice how it shoves me back on the skis – definitely not a casual fun plinker.

I did also have the chance to Shoot the S18/1000 Solothrun you can see in the video, which was a far nicer gun. I am curious how both of these compare to the Russian PTRS and PTRD rifles, as well as the Boys and Mauser T-Gewehr, and looking forward to finding an opportunity to try those out as well…


  1. My L39, serial 25XX, has two recoil spades on the mount which you drop to the ground by pulling a horizontal lock pin. These spades have little hydraulic cylinders connecting them to the mount which markedly reduce the apparent recoil to the shooter.

    Without the spades, with original Rheinmetall ammunition, my Lahti will shove a 200 pound shooter back three feet – with the gas system fully engaged. Hard on the stomach!

    • Another possible way to reduce recoil from here:

      As mentioned L-39 was gas-action semiautomatic, but it wasn’t purely semiautomatic in common sense meaning of the term. When a shot was fired and the bolt retreated back, it didn’t return forward for next shot until being released with a switch located front part of the weapon’s pistol grip. Usually releasing the bolt was done just immediately firing the shot, as this reduced the feel of recoil. Mechanism of L-39 was loaded from the crank-like handle located in right side of the weapon. The weapon fired from the closed bolt. Presumably the bolt not returning forward had been added design to improve cooling of the weapon.

  2. I’m sort of jealous – and not jealous.

    I damaged my neck with recoil 25+ years back, and it still gives me trouble, and keeps my chiropractor in work.

    I think (I need to check with Chinn) that the Lahti and the solothurn with their S18/1000 round were the hardest hitting of the easily portable 20mm cannon, with around twice the muzzle energy of the Oerlikon SSG 36.

    Although they were rapidly overtaken by tank armour, and displaced by shaped charge projectiles, the big rifles still seem to have found a niche in countering low aircraft and later helicopters, along with lighter armoured and soft skinned vehicles.

    I don’t know how the cannon compare for felt recoil with the likes of .55 Boys and the US .60 anti tank; probably very similar, and at the limits of a soldier’s capacity to tolerate it.

    I’m guessing that with the Solothurn being recoil operated, that you got the full benefit of its firing while running forward – so that you got almost half of the recoil impulse before ignition.

    With properly engineered gas operated guns, the acceleration of the gas system also works to spread the recoil impulse over a longer period of time – you really did get the mucky end of the stick with the L39.

    I know it’s easy to say when it’s not my gun and I’m not paying for the brass, but I value the integrity of my spine more than I do any brass case… a few pillows and a padded sack as a case catcher might be a fair compromise between the two?

    • BTW: Why the Britain uses two different anti-tank rounds: .55 Boys and 15mm BESA? You can say that in Soviet Union too were 2 different anti-tank rounds: 12,7×108 and 14,5×114 but in fact the first was developed for anti-aircraft purpose – the British has .5 Vickers for this so why they press into service both .55 Boys and 15mm BESA?

      • The .55 Boys round was developed by a team at Enfield for the AT rifle. (Originally named the Stanchion, but when Capt. Boys, the team leader, died unexpectedly a few days before the first trials, they named it after him as a memorial.)

        The 15mm Besa round was for the Besa heavy MG developed by Brno (Czechoslovakia) as a vehicle MG mainly intended as the main armament of armored cars. (There was a ground gun version, but it was rare.)

        The 15mm Besa round, like the 7.9 x 57mm (Mauser) rifle round used by the standard rifle-caliber Besa MG used as a tank MG by the British, was adopted simply because the gun had been designed around it, and just having the ammunition for it in the supply chain was less aggravation than trying to redesign the beast to use another cartridge, like the .55in.

        I’m not even sure that would be possible, as the 15mm round is physically a good bit larger than the .55in is, as this photo shows;

        From left to right, they are the .55in AP, the .55in AP tracer, and the 15mm Besa AP (this is a “drill” cartridge- notice the holes).

        The 15mm also fired a much heavier projectile with a considerably heavier powder charge. It was less a “heavy MG” than a machine cannon that just happened to fire solid shot exclusively.

        Add in altering the recoil masses, spring balances and etc., for the lighter “load factors” of the .55in, and it wouldn’t have been worth the effort.

        The .55in round, BTW, isn’t too different dimensionally from the American .50 BMG (12.7 x 99mm). I know at least some surviving .55 Boys rifles have been rechambered to .50 BMG for “shooting” purposes, as .50 ammunition is still produced, and .55in Boys rounds, or even empty cartridge cases, are in the collector category.

        As for modifying the Boys to 15mm… umm, no.

        There were enough broken collarbones in the war as it was.



        • @eon

          The Boys rechambering in .50 BMG is not ONLY due to .55 being too rare to shoot. It’s just .05 inch but still ABOVE the cut-out for Destructive Devices, while .50 BMG is still legitimate sporting caliber. So even if the .55 Boys was still available, it’s easier and cheaper to shoot .50 BMG in it, without bothering with federal registration, 200$ stamps and whatnot.
          American readers – correct me if I get it wrong?

        • Building a workable ATR to fire the 15mm BESA cartridge would have been possible, though. It was less powerful than the 20x138mmB Long Solothurn, which the Lahti ATR and the Solothurn S18/1000 (and the S18/1100 selective fire autocannon) were chambered for. However, it would have required a completely new design, since the Boys design would not have been up to such a strong cartridge.

          The S18/1100, by they way, is an interesting sidenote to the history of ATRs. Developed as a “universal cannon” by Solothurn, it was selective fire and was designed to be used as an AA gun as well (on a tripod of course). In theory it could still be fired from a bipod like the S18/1000. I wonder how that might have worked for the shooter in full auto… In practice it was used as a vehicle mounted cannon by the Italians and used in semi-auto mode even then, since the dispersion in full auto was quite large.

          • The 15×104 BESA is similar (at least in terms of dimensions) to Soviet 14,5×114 round, if the powder charge is similar too then the ATR for 15mm BESA should be similar in size and weight to PTRD or PTRS.

          • The L39 was also later produced as a selective fire gun, along with a way of mounting it onto a tree stump as an improvised pedesatal.

            I gather that the receivers were not up to sustained full auto use.

          • The L39/44 selective fire Lahti ATR never worked properly because of the too weak receiver, like you wrote. There were even attempts in the 1950s to strengthen the receiver, but they didn’t work, either. So finally all the weapons were converted back to semi-auto only. You can read all about it here:

      • @Daweo
        This was not the only seemingly mindless duplication in British Army supply: 9 mm MkIIz (aka Luger) and .380 revolver is also such pair, and so was .303 vs. 7.9 mm Mk Iz, both rifle-caliber rounds used paralelly. In the Boys vs. 15 mm pait it was because they were two separate programs, never intended to meet one another side-by-side. The .55 Boys was a locally-designed repeater, while 15 mm Besa came ready from Czechoslovakia with the heavy machine gun ZB-60 – a scaled-up version of the Besa Mk I which was in fact a British copy of the Czechoslovakian ZB-53. That’s why they also maintained two rifle-caliber machine gun rounds all through the war: the .303-in and 7.9 Mk Iz for the (small) Besa. Both Besa machineguns came too late to be converted to British calibers, like the ZGB-34, later to be known as Bren. Mind you, it took SEVEN years from 1929 to 1936 to co-ax the ZB-26 to reliably operate with the Brit round, which mandated a thorough, wholesale re-design of the gun – I doubt if there were more than 5 bits of metal interchangeable between the Czech and British LMGs. The British decided, that they have no time to waste in 1938, and they were right. So they just accepted the Czechoslovakian licences and started to manufacture ZB-53 and ZB-60 as is, with their metric caliber nitrocellulose ammunition. Anyway, they were intended to be used for tanks only, so the supply was much more streamlined than the .303. Same thing later on with tank Brownings, which came with American lend-lease tanks – but of course these were delivered with mountains of ammunition, without burdening the British industry.

          • I took a walk onto the backstop of an abandoned first and second world war rifle range yesterday.

            It wasn’t the most exciting – no .577, .450 or .400 bullets, like one of the other old range I’m sometimes past.

            just .303 and a few .45 fmj pistol bullets, I’m not sure whether from a thompson or a 1911.

            It’s surprising how many 215 grain round .303 hollow points some of the old ranges contain (left over boer war stocks?).

            Incidentally, I’ve got a hollow point .577 schnieder bullet sat on my widow…

        • Since the supply of 7.92mm and 15mm ammunition for both types of Besa MG was destined almost solely for the armored regiments, which had specialized and exclusive logistical requirements anyway, the British Army’s supply train was already well-prepared to deal with the additional demands. Also, it was considered that advantage could be taken of captured German 7.92mm ammunition.

  3. I’m curious as to how the various AT cartridges compare to each other and the 20mm Orlikon round from the WWII Navy AA guns. Do you have anything in that vein?


  4. OUCH! I assume that the Type 97 anti-tank rifle would be worse than this, though if the Lahti and the Type 97 were to encounter each other, I have no idea who would win…

    • If we will use loose definition of anti-tank rifle we can consider 2.8 cm sPzB 41 as a rifle (it was called by Germans Panzerbüchse i.e. anti-tank rifle).

      • Well, it did have an emergent caliber of 2cm (Gerlich taper-bore system). But considering that it massed 229 kg (505 lbs) on its standard carriage, and still went 139 kg (306 lbs) on its “light” airborne carriage (118 kg/260 lbs if you left the rubber-tired wheels off), it definitely wasn’t in the “man-portable” category, which was more-or-less what divided the “anti-tank rifles” from the “anti-tank guns”.



        • Ironically, the Solothurn S18/1000 was called the “2,0 cm PaK” (20mm anti-tank gun) in many German wartime documents. It might have even been the official designation, but I’m not sure of that. It and the Lahti L39 required two men to carry them in any case, so they were only borderline “man portable” as well.

  5. Oh man…! That’s gotta hurt! I’ve always shied away from .50 BMG and .338 Lapua and .300 Win Mag because I’m sure I’d get a detached retina or something from shooting it… Can’t image the Lahti 39 20mm!!! On the other hand, I’d sure like a Solothurn for my bicycle like the Swiss used to use! Heh.

  6. I don’t need a gun like that, I have no business wasting money on a gun like that, and my wife would kill me if a got one…

    …and I really want one. I’m partial to the PTRS, but I’d take an L39 or a Boys.
    Maybe after I invent the cure for the common cold.

  7. You all seem to forget the Carl Gustav 20 mm Recoilless Anti-Tank rifle; !!!
    Infinitely more fun to shoot, much lighter at 11 kilos to carry and harder hitting than any of the other 20 mms. IIRC, the thing fired a 110 gram shot at 3,100 FPS? But you should look those numbers up just to be sure. As you can see from the video, it is nearly recoilless and in my estimation after shooting it has much less recoil than a 300 Win Mag in a 9 pound rifle. Think what a dandy sniper rifle it would make today! Modern flash and smoke free propellants, say 1000 M/S MV and a long ogive 125 gram guided projectile???

    • I didn’t forget about it, but nobody just brought it up. It wasn’t used in combat like the other ATRs mentioned here. An innovative weapon for its day, no doubt about it, but since it’s a recoilless rifle, the huge backblast could not be really avoided even with modern propellants.

      Its legacy of course lives on in the 84mm Carl Gustav recoilless rifle still used in many countries around the world. The US army adopted it only in 1990s for special forces, and currently it is widely deployed in Afghanistan, where its used as a direct fire support weapon.

      • I humped a Carl Gustav 84mm RR, among other support weapons, during the time I was “in”. An excellent and versatile man-portable anti-tank / multi-purpose weapon system, to be sure, and not unduly heavy — but bulky and a little clumsy, due mainly to the added mass necessitated by the venturi at the rear. The battlefield signature is, of course, fairly significant due to the backblast, with everything that implies.

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