Inside the Lahti L-39 Anti-Tank Rifle Build

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.

http://www.youtube.com/watch?v=IrWq7W5qmP4

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.

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