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Inside the Lahti L-39 Anti-Tank Rifle Build

by Will Hayden   |  September 5th, 2011 68

My first thought when the client, Spencer, brought in the Finnish 20 mm Lahti L-39 anti-tank rifle you saw on last week’s show, was that I did not want to shoot the thing. Any firearm that needs to be attached to a plank so it doesn’t drive your shoulder directly into your backside gives me a little trepidation.

I would hate to think of anyone shooting it without the lock bars on a skid board. All of the accounts that we read during the process said that this gun will break your shoulder if you allow your body to absorb the full recoil. It’s a huge gun with a lot of firepower, not to mention a lot of history.

It was developed in Finland by Aimo Lahti around 1939 in response to the many doubts of the original idea of the 13 mm anti-tank machine gun. After testing, those boys found that the 20 mm offered better penetration than its anti-tank counterparts. It was put into action in several wars including World War II and the Winter War.

Nowadays, the de-militarized version of this big boy are pretty rare. When you are able to reactivate one, like we did, the value skyrockets. Which is why Flem’s welding was key to this project.

Flem is a gifted welder, bottom line. But when you have a weapon of that size and explosive potential you have to double check everything. As you saw on the show, we had a rifle sonogram performed to ensure the welds.

After we were 110 percent certain the welds were properly in place, we ran an analytical stress screening to determine the varying degrees of temper throughout the receiver. In other words, we were checking to make sure the metal in the gun wasn’t hard where the welds were and then softer a few inches away. That will end up warping, stretching or cracking the receiver
and, trust me, you don’t want that to happen.

Once we had the gun put together and ready to roll we had to find a way to mount it. The Lahti 20 mm is about just over 7 feet long–tremendous length–and it weighs about 140 pounds all together. It’s just a beast to try to move that thing around. So, the mount was critical to being able to make this project work. Otherwise, like I said, it takes a good amount of effort to keep the gun from smacking you into the dirt. We actually used a pedestal from a MG 42 dual mount and bolted it onto the truck and a vehicular mount to attach the Lahti.

Once we had it ready we just had to attach the gun, dial it in on target and then anyone could just jump in behind it and pull the trigger.

Next, we had to tackle finding ammunition. If you watched the entire show, you saw that Charlie had a tough time tracking down what we needed. But he worked hard and found a mixed bag case with about 100 surplus rounds. Some of the ammo was Finnish, some of it was Swedish and there were others that we couldn’t identify. Some were armor piercing rounds, some were high explosive (H.E.), some others were just downright weird–they had a lightweight head with a big hollow point.

Most of the ammo was from World War II–it was at least 60 years old–which meant we had a lot of problems with the cases breaking and sticking. The crew polished them as much as we could, but some of the odd ball manufactured cartridges didn’t cycle at all. We just used it as a single shot at that point.

Once we had it shooting, it was time to show it off to Spencer and his 82-year-old Godfather who survived 25 or 30 combat bombing runs during his time in service. The man basically lived his life with just a little piece of plexiglass between him and the anti-aircraft cannons and big caliber guns that were sending rounds his way. The reaction on his face made it that much better. It was a great day, and a great project for the whole team at Red Jacket.

See ya’ll next week.


  • Larry Huffman

    A great show to watch. It was surprising to see the penetration ability of the round, but reminds me that in the early days of WWII, a 37mm was considered a fully capable antitank gun in the U.S. Army.

    • Will Hayden

      One shot we made , after going through the brake hub [rotor?] , then the frame of the car , the round went about 2 feet into the dirt . We shot about 80 rounds that day , tore up all kinds of stuff , it's a hell of a "rifle"

      • Curious George

        Whats the deal with the H.E rounds for that, isn't each one considered a D.D and requires a 200 tax stamp?

        • Curious George

          Also, you guys should check out this bad bitch.
          Those guys have been trying to sell it for months now. Would love to see it on the show. 65 round drum, 20mm, full-auto, you guys could make a hell of a mess with that thing.

          • Arnold

            Full auto yes, but the cartridge is not near as powerful as the round fired by the Lahti, and Solothurn S18-1000 rifles. (wouldn't turn one down tho,,,,)

        • Mickey

          A projectile is only considered a D.D. if it has more than 1/4 ounce of explosive or incendiary media in it. The majority of 20mm rounds, including US 20x102mm rounds just skirt below this level, and are therefore not D.D.s themselves. The ATF actually makes reference to this on page 17 of their NFA handbook ATF E-Publication 5320.8 Revised: April 2009

        • Arnold

          That is correct, each projectile has to be numbered, and papered. Then after being fired, there is a report to fill out showing that they had been expended. The tax per round is only if one does not have the appropriate dealers license, and has paid the occupational tax. otherwise, its $200 per shot for H.E.

  • gulluman

    wow,i want to know more

  • http://Facebook Dale Hord

    That was a great show. Really enjoy watching you come up with the Quad MG-42's, the Tri-M16 but this was a piece of History that you brought back to life and an amazing weapon to say the least. Really enjoying the show since it was told to me from a friend. Deep up the great work every!! Really interested in seeing what you have planned in the future!!

    • http://Facebook Dale Hord

      I meant to say "Keep up the great work!!" Sorry didn't proof read before posting.

  • Tim Sheahon

    I remember back in the early 60's , those thing were selling for about $500, delivered. There was another one too, a 25mm from one of the Baltic countries on a wheeled carriage. If only I had the foresight…. But M! Garands were going for $79 or $80 too .Lugers and P-38s for $49 to $60. Interarms,, Century, and a couple of others were selling that stuff dirt cheap.

  • Justin R Brown

    Its just an awesome feat to have ANTI-TANK and RIFLE to be in the same sentence. I've shot my share of weapon systems in my 8 years of the military from 9mm to a howitzer. The first thing that comes to mind for me when I think of anti-tank is something like a cannon. Awesomely it can be done with a rifle!!!! If every mind on the planet worked toward one common goal And there were only friendlies I can only imagine what we could accomplish! On the other hand if that were to happen we wouldn't have a use for anti-tank rifles which kind of makes me sad. Love the show love what y'all have done for our military so keep up the good work.

    • Will Hayden

      That first sentence LOL , I felt the exact same way :) It was strange , shouldering the weapon , knowing just how much destruction it was capable of . I mean , tanks ???

      • Arnold

        The L-39 was designed for use against the Soviet BT-5, BT-7, and T-26 tanks which are all very light, and typical of tanks of the 30's. Its not up to a modern tank, tho it could be well used in harassing one.

  • mintukumar

    hello friendz

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  • alejandro

    caramba muy buena

  • Diana J. (Mason) Mea

    Good evening,

    My dream is to shoot one of your weapons? I love your show . . . it's obvious all of you are compassionate about what you do. It's so important to enjoy what you do. What a blessing! Every time I watch your show I end up with a smile on my face, thank you.

    God bless!

    • Will Hayden

      well , come down to my Birthday party in june , our yearly B-Bash . It's Sat. of the first full weekend in June . We bring out all our mg's and let folks have at it . We've been doing it for 6 years now , my way of saying "thank you" to our customers and friends . We run it through The AKForum , the S-12 Forum and UziTalk , hang out on one of them next spring and we'll get you an invitation . Will

  • nicole mason

    Mr.Hayden, I personally want to thank you for your wonderful show.. My boyfriend and I watch it reliously, u have some crazy ideas with absolutly wonderful results, your team of workers seem to be the best in what they do.. keep up the awsome work ya'll do..

    • Will Hayden

      Thank you Nicole , I have good people with me , that's all it is . Will

  • http://facebook Vannak Mao

    I really like your ability, always dream like this if i can i going to make all think in my dream.

  • Douglas Benne

    What type of license do you need to even own a Lahti?

    • Arnold

      No license needed, it has to be registered to the owner. a duplicate form finger print cards, and mugshots, local LEO signature, and then another investigation by the FBI +plus $200. transfer tax. If all goes well you get to take it home in about 6 weeks.

  • Jimmy Repass

    want the 12 gauge gatling gun(aka Street Sweeper)1400 rounds per minute….:)

  • Bruce Parker

    Will, my 9yr old son and I Love tbe show. We have the entire series on DVR. We even got him 3 different T-shirts which are his favorites. Tell me, What is the History of the name of your business and the Redcoat In the Lobby? Is it British Revolutionary War era?…

    • Will Hayden

      Thank you Bruce . Red Jacket is my name [ Choctaw , in the language it's Oshkhouma], the coat is just something I picked up along the way It's 46th Regiment of Foot , 1750's era . French and Indian War period .

  • mitch

    your welder "phlem" is not very good at actual welding. you should not call him a "welder". he is what real welders call a "dobber"

    • Will Hayden

      Fleming is a very good welder , one of the best I've seen .He also has a great work and personal ethic and great attitude . He would never say the following , so I'm going to step in for him . Mitch , it sounds like you not only know all there is to know about welding and fabrication but also know how to convey your vast knowledge in a concise and articulate manner . No doubt this has served you well and is responsible for your wide fame and success . I applaud your achievements , particularly the way you sit behind a screen and sling shit at one of the finest men I've ever known , one who manages to get up and to work everyday in spite of having had 6 helicopters shot out from under him in combat and having had multiple surgery's to his neck and back . You're really going to pass judgment on a man based on 23 seconds of footage ? I see his his work daily , 60 hours a week . He does fine .

      • Karl

        It is hard to weld metal, especially thin stock like a receiver without getting some slag or porocity in the weld. Even certified welders have that problem. Most never realize it since few welds are x-rayed or inspected with other NDT tests.

      • Ken Maiden

        Mr. Hayden,

        Enjoy the show. Keep up the good work.

        Now, I wish to thank you for putting mitch in his place. I hope to someday visit your shop, hopefully with a project.

  • mitch

    also, your guns are really nice but items like the articulating arm for the chopper are horrible. i mean yeah , it swiveled and held the gun but why not make it into a peice of art too?? you should invest in a nice tubing bender and hire a real welder and stop making mounts and such out of steel that is meant for building trailers.

  • Will Hayden

    well , that's a lot . miss a couple days … Anyway , thank you guy's , this was a really great project for us , there's nothing better then bringing a piece of history back to life . It's the kind of project everyone in the shop wants to get in on .

  • Mark Cooper

    I don't like your show ,I absolutely love it! My brother had a gunsmithng busisness so I know what meticuous work that go into those projects .He also is a talented welder and mechanic but did not keep his gun busisness . Just had to tell you again how much I love the show . Mark

    • Will Hayden

      Thank you Mark , my best to you and your brother . Will

  • Martin frank

    The lahti episode was very cool. I always wanted to see a Russian ptrd or ptrs in action but you guys went even bigger than the 14.5mm ! The fact that flem welded it back together out of a de-milled parts kit is amazing, and a testament to flem's outstanding welding skills. I love the show and it gets so many people interested in firearms in a positive and fun way

    • Will Hayden

      Thank you Martin , he's a hell of a guy . I get behind a LOT of his work :) . Will

  • http://corn,beans,spentbrass,anemptypageandadeadline Frank W. James

    The Old Western Scrounger used to sell a press, the dies, the primers and some of the propellants needed to reload a 20mm Lahti case. Years ago a friend and I pulled a couple of cases and discovered it is a duplex load with a little snuff-like bag positioned immediately over the primer. The big problem with reloading the 20mm Lahti is the primers on the WWII ammo is all mercuric and after firing the mercury attacks the brass making it difficult to continuously reload that stuff. Still, it's always good to save the brass.

    Me? Yeah, I've played with a Lahti a time or two……in a gravel pit in Indiana. We found the AP round would penetrate 13" of solid limestone, er…at least…

    All The Best,

    Frank W. James

    • Will Hayden

      Reloading for it's ….interesting . I'm looking into doing one in the 20mm vulcan , ease ammo issue's .

      • http://corn,beans,spentbrass,anemptypageandadeadline Frank W. James

        If I remember correctly (and that's ALWAYS a challenge) the driving bands on the 20mm vulcan are wider than the bullet diameter for the Lahti. I think you have to turn those driving bands down a few thousands on the 20mm vulcan projectiles in order to use them for reloading the Lahti 20mm.

        I didn't catch all of your show on the Lahti, but from what I saw you certainly went about rebuilding it in the correct manner. I was impressed. Good job, very professional.

        A big problem with reloading the Lahti is finding the correct propellant because it really needs a S-L-O-W burning rate propellant and even then you're going to be loading 'pud' loads; I wouldn't recommend 'Hot' in any way, shape or form.

        I think Dave Cumberland sold his business, THE OLD WESTERN SCROUNGER, a few years ago because I haven't seen him at the Shot Show for a couple of years, but I think the business is still operating. I'm just not sure. I know that's not much help, but still I know they offered that stuff at one time…

        All The Best,

        Frank W. James

  • John Enockson

    I was curious about your rotating shotgun arraignment. Since it was fed by three radial magazines and rotating at full speed was it possible the centrifugal force involved could affect the rate at which the rounds chambered? Did those magazines have stronger springs to compensate or were standard units used?

    • Will Hayden

      standard , we'll do a write up on it shortly.

  • Kristopher

    I own an original Lahti.

    Here is an old video ( 1 of 4 ) of me shooting it for the first time ( and learning the hard way to not put my hand over the ejector port, or to allow the muzzle brake to point downwards )

    It is not a shoulder breaker. If you fire it from the sled mount, it tends to shove you back, rather than slam and hurt you. 140 pounds of rifle resists recoil quite a bit.

    The most disconcerting thing about firing it is that it has a tendency to twist to one side as the projo engages the rifling and starts to rotate on its way down the bore.

    • Will Hayden

      Cool , never noticed the twisting , then again we did most of our firing from the pedestal mount .

  • Cathy Kee

    Hi, I watch your show every week….love love it. I have learned a lot about different type of firearms and wantt to say thanks to you and your crew. I am from Texas and guns are an everyday thing here. Keep making dreams come true,thanks for keeping it real.

  • Witt Sullivan

    I can't wait to read more about the rotating shotgun system, it was fantastic! I've seen pics of home made mounts for AK's and SKS's that were hand cranked that were okay, but not like that. :) You could put the mounting system on the market for people who own a few AK-style weapons or adapt it for AR-15 style rifles by using the rail on top of the receiver mated with the adapter you use for the Saiga Masterkey.

  • Douglas May, Sr.

    Personally I hope you continue to work on the 12ga Gatling design, a belt fed 12ga minigun would be awesome and should be do-able, altho the rim of the shotgun shell would present some problems. Think military 12ga minigun shooting slugs or buckshot, or a mix! Awesome close range firepower!

    I don't know how much say you have in the final show Will, but there should have been some discussion of the differences between 20mm Lahti and the 20mm our military currently fires. I don't have alot of knowledge of anything bigger than 50 BMG so I was wondering myself during the episode.

    • Kristopher

      The current 20mm Vulcan round is shorter and a bit fatter than the 20mmx138belted round the Lahti fires. It also has a bit higher energy than the old WWII round.

      One person on the Obscure-Reference D.D. bulletin board has converted a Lahti to fire the much cheaper Vulcan round.

      Those "hollow-point" rounds talked about were probably reloads using surplus Vulcan HE projos loaded into Lahti brass. The fuse and explosives were removed ( probably burned ) when the rounds were de-milled.

      I reload my brass with aluminum tipped Vulcan practice projectiles.

  • Will

    In the novel "Unintended Consequences" by John Ross, he goes into considerable detail about the ammo for the Lahti, including modding 20mm Vulcan for it. As far as I know, he was very careful to ensure all such data contained in his book was accurate. My copy never returned, so I can't refer to it for specifics. Offhand, this might be the only book I can think of that could be said to be accurate about firearms.

  • Rick Hanson

    Will, like the show, and and am impressed with the gunmaking skills of your people, but please buy Vince a set of depth mics.

    They are only a couple of hundreds bucks for a good set of 0" to 6" Starretts, and they give you a much truer measurement than a set of calipers, especially when having to have the very accurate measurements needed when headspacing barrels and such.

    A set of inside mics are really handy too.

    Both of those tools should be standard equipment in any gunsmithing/gunmaking shop.

  • mitch

    i tried to reply to your defensive comments up there but it didnt work. anyway, will, calm down, dont be so defensive, i would never judge him from footage expecially discover channels footage. (o and thank him a million times for his service) I was judging that weld tho because it only took 20 seconds to show all the holes in it. Ive been in manufacturing since 1981 and all (100%) of our welds have to be tested in several ways so i know a crappy weld when i see one. So anyway yeah i am sure phlem is a great guy and if he did not do the weld that was shown on tv then boo dc for showing it as his. either way it was full of porosity and i would imagine dangerous on a gun. thank you for applauding my achievements, I am all gimped up from an accident when i was 12 years old and i get up and go every morning too.

  • enuf.istoomuch

    De-militarizing perfectly good firearms is just a crying shame. It was great to see an old workhorse from the Good Guys side of the equation brought back to life!

    Nicely done!

  • Jeff Wright

    I wonder how far the rifle concept might be taken. The smart shell tech for the Excalibur–could that be scaled down for directed bullets…

    A little OT

    There was this crossbow set up on a Military Channel special–Weapon Masters special where several gyros were used and a steadycam armature to boot, not unlike what is seen here:

    I wonder if a variation where a steady cam can be quick released from a helicopter door and carried right out into the filed might be possible.

    Also, on the episode where you had four machine guns slaved together. I wonder if having each machine gun atop its own stalk to a common base might dampen out any vibrations that causes one gun's recoil to interfere in a neighbors operation. Two guns are fine, any more than that and things get interesting unless each is isolated a bit, one would think…

  • Arnold

    The recoil isnt that bad, mostly a good solid shove. The recoil of a Boys rifle is much harsher.

  • tim scarborough

    I just bought a Lahti L-39 this weekend on Gunbroker from Havana Florida. The rifle comes with 2 mags. I have another 7 mags coming from Ma. Who would have the best price on ammunition for the Lahti. I have seen several different 20mm rounds available, but i think most are a shorter 20mm round. i think i am looking for the 20mmx138 … i would appreciate any help… Thanks Tim …

    • Arnold

      You need 20x138B ammo, nothing else will fit, or work unless the gun is converted to fire them. Ammo is where you find it, and costs whatever its present owner wants for it. Not uncommon to pay $60.00 or more per shot for good clean ammo, tho that can vary widely.

  • Arnold

    The two original test guns were chambered for two different rounds, one, the 13.2×118, and the other 20×113. The 13.2 could penetrate well enough, but the 20mm caused more damage, so it was chosen. It did well enough, but was found wanting, so later, it was discarded in favor of the 20x138B (which was not found wanting)

  • Shootist

    I always thought one of these would be good hunting … dinosaurs, maybe. Regardless, I'd love to shoot one. The 20mm Lahti must make the Barrett M-82 seem like an M-16, and the Barrett is loads of fun to shoot.

  • FrankOK

    About 20 years ago, I assisted a couple of friends in making one of these a single-shot .50 BMG from a pile of parts and pieces another acquired. Work consisted of a new 48" stainless barrel and bushing the firing pin hole in one of the two bolts to a smaller size with an silver-soldered-in insert plus much welding, checking, hand wringing and general shop hack-and-gouge-to-fit practice. Very accurate but too damned heavy!

    "Twas fun but a novelty only.

  • Guest

    Saw a Lahti perched atop a display case in a North Carolina gun shop many, many years ago. I was struck by the sheer size of it. One of the unique features about this particular AT rifle, is that it is semi-automatic. Most AT followed the original Mauser pattern from WWI, being bolt actions.

    This would be a potentially life saving feature. Cruiser tanks, or Fast Tanks as the Russians called them, were lightly armored but relatively fast. Example cited previously: BT-5. A flank shot would have been quite a challenge. More heavily armored infantry tanks, like the Matilda, were slow but more heavily armored. Even so a flank or stern shot could prove to be lethal.

    Great show, Will, always enjoy watching your handiwork in action.

  • Al Brady

    Remembering in 1962, Gun World probably or maybe another gun type magazine had Lahtis advertised for $99 complete in the chest with all accessories and appropriate 20 mm rounds at $1 each, 10 for $9 or 100 for $81. Those fond memories just make ya class politicians lower than bankers, lawyers or skunks. Thanks for a very enjoyable program and my appreciation to your crew / family. Good work with good people make a good life!

  • james

    See you lost your F.F.L lic.

  • Marco

    seeing all these comments I am proud to be finnish!! we made some awesome guns at russian war and made russians to pay for invasing our country, I remember raatteentie and other great victories..

  • John1458

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  • John1458


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  • John1458

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  • John1458


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