Swedish Antiaircraft Artillery: Bofors 40mm Automatic Gun M1

Note: In the video I mistakenly describe this as a two-stamp NFA gun. It is actually deactivated, and thus does not require a tax stamp. Sorry for the mistake!

RIA’s catalog page for this cannon

The Swedish Bofors company developed their 40mm antiaircraft gun in the 1930s, and it would go on to be one of the most successful weapon designs in modern history. Used by both sides in WWII and in all theaters, improved versions of the 40mm Bofors gun continue to serve in military front lines to this very day. In the US, they comprise part of the armament on the AC-130 Spectre gunships, for example.

This particular gun is a WW2 vintage piece, made in Sweden. Most of the examples used by the United States were made under license by Chrysler, the car company. Something like 60,000 were produced during the war, mostly for naval use. These guns would be a mainstay of American vessels’ air defense against Japanese Kamikaze attacks.


  1. They do. But they are expensive and almost artisan level quality. Go with standard 40MM HE-Tracer should get the job done at a reasonable price. But avoid using it on Sqirrels as that would be considered bad form, overkill, that sort of thing.

    Rats and Squirrels are more a 20MM problem. Chipmunks? 50 cal HBMG.

      • Coyotes are great deal larger than squirrels or gophers, and require a proportionally more destructive solution.

        For that type of critter, I wouldn’t settle for anything less than a nuclear-tipped Nike Hercules missile. It’s the only way to be sure.

  2. The alternating firing barrels on the twin mounts for these were the inspiration for the gun mounts on a certain famous sci-fi spaceship, if you weren’t aware.

  3. The iconic Naval twin mount differed from the land version in that there were water cooling jackets on the barrels. As mentioned in the video there was a standard and a long cartridge. I have a standard length casing from my time in the Navy and it measures 12″. I’m guessing the long version is probably 15″ long.

  4. Ian mistakenly refers to it as a two-stamp NFA gun, RIA mistakenly refers to it as a Chrysler-built gun. So much mistaking going on, except with how awesome the thing is.

    • Two great scenes, really — Ackroyd’s “Do Not!” briefing and then Ned Beatty’s “shootout” with the Japanese sub.

  5. I’d guess the ballistics were at least equivalent to all the ‘2 pounder,’ 37mm antitank guns of the early WWII timeframe? I’m a little surprised that these weren’t employed as vehicle mounted antitank weapons.

    • They are used on vehicles today, the very modern Swedish CV9040 infantry combat vehicle has a 40mm Bofors. Other countries fielding the same chassis have generally opted for smaller calibres like 30 or 35mm, because that works well enough on light armoured targets and allows you to carry much more ammo on board.

      I guess much of the same applied in WWII: Light tanks fared poorly against MBTs, and a vehicle with a 40mm cannon would basically be a light tank. The AT guns of similar calibre were generally inadequate on frontal shots on proper tanks, so had to rely on camouflage and careful placement to get flank or rear shots in. Easier to hide a relatively small gun on a low mount than to hide a much tallet vehicle with a gun on top.

    • My definition would not rely so much on caliber (although 20mm is conventional border line) but nature of cycle in following of previous one. If there is natural firing follow-up without cycle interruption than you have Machinegun. I do not think that rate of fire has anything to do with it. Need to keep ROF in lower range leads to doubling or quadrupling up barrels.

      For instance, the widespread ZSU-23-2, although already in field of canon (using conventional definition) by caliber, is still a machinegun. Note that while its natural rate of fire is high it has limitation in barrel life span.

      • Well, what is a gun and what is a cannon depends 🙂 Finnish military had prior to WW2 that a weapon with a mallible bullet which fits into rifling = rifle. All others (usually bigger) guns with non-mallible projectiles with thick copper rings are duns/cannons. Everything went OK until finns received Messerschmitt Bf-109G-6 fighters which had MG-131 13mm machineguns. Their ammo were cast stuff and had those copper rings to hit the rifling.

        After the war FinMil decided that everything from 20mm and on is cannon, under that rifle.

  6. From a defense industry stand point have heard it said that 20mm and up is considered cannon. Rapid fire anything below that is a machine gun. Your mileage may vary….

  7. Argh I feel old now, I was trained for this cannon in national service back in -80. 40ItK36 is name in Finnish service, had better sights though, and mechanical lead calculator.
    Fun to shoot, and darn accurate up to 2,5 kilometers when shooting direct targets.

  8. How does one cock a Bofors? I understand it’s a falling block, but how do you load the 1st round.


    P.S. a 40mm Bofors is part of the final chapter of the book version of “James Bond: Diamonds are Forever”

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