23mm Madsen (Sectioned)

This cartridge is identified as a Danish 23mm Madsen. The headstamp is MADSEN over 23MM (12 o’clock) K (9 o’clock) 37 (3 o’clock). Whatever was at the 6 o’clock position was removed when it was sectrioned. The case measures 106mm long. Additional info would be appreciated.

I also have a sectioned example of that round.

From an article on collecting 23-28mm cartridges published in the July issue of The Cartridge Researcher, the bulletin of ECRA:

"…the 23mm Madsen, which used a 23x106 cartridge formed by necking-out and shortening the case of the popular 20x120 Madsen round; the guns were identical, except for the barrel. The idea was to trade velocity for high-explosive content to increase the effectiveness of the gun in its aircraft applications; the HE shell contained double the HE of the 20mm. The 23mm Madsen featured in various experimental installations, but never made it into service except

Thanks for the information, Tony. No wonder I was coming up with nothing in my search.

Some examples

From an undated 1930s Kynoch catalogue I have entitled “Cartridges for Military Rifles and Machine Guns”

As you can see, it lists several loads in addition to the Explosive.


Thanks Tony, that’s helpful - you learn something every day!

There is one reported combat use of the 23mm Madsen, although I don’t believe it. One was supposedly fitted to a D.520 fighter of the French air force in June 1940 and sent off to attack German armour. I don’t believe this for several reasons: first, even if available with armour-piercing ammunition (which seems unlikely), the penetration of the medium-velocity projectile would probably have been worse than that of the plane’s usual high-velocity 20mm Hispano; secondly, I doubt that the bulky Madsen receiver would have fitted in the same limited space behind the engine as the slim Hispano; and thirdly, Hispano themselves had 23mm guns under development at that time, the HS 406/407. These fired very powerful, high-velocity 23x122 ammunition (the ballistics were the same as the Soviet VYa) which would certainly have been effective against most 1940 tanks. So my vote’s for the HS. Sadly, the plane was shot down before achieving anything.

I agree it sounds unlikely. Do you know if the 23mm Madsen utilised the same receiver as the 20mm?

As you know, there was a lot of British military interest in the 20mm Madsen in the early thirties. They particularly liked the short inboard receiver length of the Madsen. However the only reference I have found to the 23mm in Ordnance Committee papers (OB Procs. etc) is in connection with development of the explosive shell for the .661" for the Admiralty. In Memo No.B33,226 of Feb 1937 headed “Projectiles and fuzes, Madsen’s 20mm. and 23mm. guns”, it refers to preparations for the .661" explosive shell design with an MV of 3300 fps at 25 tons and requests ICI and VA to submit suitable designs to the Superintendent of Research. Interestingly, it also mentions an order to BRNO for 15mm BESA exploasive shell.


Would the ‘K’ in the headstamp of this one indicate production by Kynoch?

Yes, Kynoch made lots of Madsen shells in various calibers. There was a great effort to get the British govt. to adopt Madsen guns.

Kynoch was actually the usual developer/manufacturer of Madsen ammunition, as they had no ammo facilities themselves.

Tony, the 23mm Madsen used the same receiver as the 20mm (only the gun barrel was different). This was quite short, but deep.

Do you have any more information about the .661 - the gun rather than the ammo?

20mm Madsen cartridges were also made by Denmark, Finland, Oerlikon and DWM.


I have a selection of both Kynoch and military drawings for the .661 case and bullets, plus some copies of OB Procs and Woolwich Research Department notes, but these are virtually all to do with the development of the ammunition. There is very little on the weapon itself.


Does anybody know why the 20x120R rimmed prototype Madsen was made first by Patronenfabrik Solothurn in 1926 (Switzerland)? How were the Swiss (or Rheinmetall) related at this time?