Ammo for Norwegian 20mm M1940 Brøndby

I came across images of the Norwegian 20mm M1940 Brøndby gun but given the location and time period I do not have the slightest idea what cartridge this gun could have been chambered for.

Does anybody have info, docs or images of the cartridge for this gun?

Here the gun:


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Is this gun really so unknown?


The gun itself is entirely new to me, so I have no clue about it or its ammunition. A search through my files only throws up this British Patent, granted to Mr Brøndby in 1934.

GB415841A(brondby).pdf (503.4 KB)

Would Norway have developed its own cartridge, or would it have used a proprietary one ?


Is there any data available concerning this gun?

The pic is all I have found.

I’ll ask a friend who specialises in everything Norwegian but can’t guarantee an answer…


I’ll ask a friend who specialises in everything Norwegian but can’t guarantee an answer…

Any luck Ole?

Waiting for a reply.
Meanwhile, it’s interesting to note that this 20mm cannon shares the rough design and the same muzzle device with Brøndby’s rifle:

Check the bottom right picture.
As well as his submachinegun:

Hoping to get a reply from my friend on what it may have been chambered in.

My first thought was a gun to shoot slag out of furnaces, but might be too easy of a guess…

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Thanks Ole.

I’ve sent an enquiry to the Norsk Bergverksmuseum but they’re closed for the holidays until next week.

Wouldn’t a gas operated gun be a bit of “too much” for a kiln gun?

I have had a response from Frode Saeland, Curator of industrial history at the Norwegian Mining Museum which has the gun. He believes that it is chambered in 20x120 Madsen, as reference was made to obtaining more ammunition from Madsen if required. The gun is actually semi-auto (it’s a scaled-up version of his rifle) and seems to have been intended for the anti-tank role. It was entirely a private venture, and the military were not interested, so it didn’t get beyond firing a few rounds.

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I have a great deal of information about this gun, including photos, some blueprints, etc., but I’ve agreed to publish them only in my book. While the materials aren’t clear its my opinion that the gun was chambered in an already available round, something that could be fired from the Madsen or Bofors.

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What is the scope of your book, nirvana?

Antitank rifles, every one that I can locate and get information about. Will be covering the weapons, ammunition, and whatever stats are out there. My focus is largely technical, in that I’m taking and obtaining detailed photos of the mechanisms of each gun, along with photos of markings and so forth. Five years in the works… And it’s a bear.

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Good luck with that!

I expect you are aware of Zaloga’s recently-published work “The Anti-Tank Rifle”, which apart from a couple of glitches does a very good job of providing an overview of the subject, how ATRs were used, and so on. His focus is on the principal weapons which saw combat, so no more than a mention of guns like the 20mm Oerlikon SSG and SSG-36 (although he does provide a section on the US experimentals). It sounds as if your book is going to be much more technical.

I hope you are going to do a better job than Zaloga of showing the ammunition: an incomplete display is here:

I am familiar with Zaloga’s book. Its a very good primer on the topic, and is somewhat analogous to the earlier Know Your Antitank Rifles book from the 1970s. He does a good job at giving a broad overview of the topic, which is good for most readers. He probably has more sense than I do, as covering just the major production guns is certainly easier than running down every rabbit hole that you come across. The US prototypes for example: I’ve got four unique guns under review, and these are just the domestically produced guns that were actually tested, nevermind the Solothurn guns that were sampled or the Boys rifles that were issued.

I will be covering ammunition in a lot more detail. I am not an “ammo guy,” and I do admit my limitations in that area. My main ally has been a friend of mine, Ken Huddle, and then information that I’ve been pulling off the internet as time permits. Its a long process, as I’m sure you know.

Yep, I’m currently working on a complete revision of my book 2000 book Rapid Fire, with far more detail about automatic cannon (20-57mm) and their ammo. It’s literally taking years, and may well end up as three volumes…

Just for the record, Zaloga makes two common errors, in stating that the Japanese 20mm Type 97 ATR was designed to fire full-auto, and that the PIAT was spring-powered.

I’ve got rapid fire. It’s a great book, although I’d have no objection to buying an updated version.

That Type 97 issue always kills me. The thing didn’t fire full auto. I’ve taken one apart to damn near every component and I can say for certain that the sear resets after each shot.

I have heard various stories to account for the “Type 97 auto” myth. One story is that a sear failed, causing the gun to empty its magazine in one burst. There are two versions of this one - the first says it happened to a senior Japanese officer trying out the gun while it was still a prototype; the other says that it was a US serviceman who experienced the same thing when testing a well-worn example. Maybe both are true.

The most likely explanation, though, is that Kawamura was asked to turn the ATR design into an automatic cannon for installing in aircraft. This he did, in two versions, for flexible and fixed mountings, and both saw service. They were adopted as the Ho-1 and Ho-3 respectively, but before adoption the automatic prototypes were apparently still referred to as the Type 97.