This is intended for people interested in the subject of military guns and their ammunition, with emphasis on automatic weapons.
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In the Flight magazine of 1 July 1955 (https://www.flightglobal.com/pdfarchive/view/1955/1955%20-%200912.html) you may find an article which includes info on a twin 34mm AA gun. This is what the article says on that:
'By the entrance to the exhibition hangar are sited two pairs of the latest 34 mm fully automatic flak guns, radar laid at jet speed. Each twin-gun has a combined rate of fire of 900 rounds a minute, a muzzle velocity of 1,000 m/sec and a practical range of 4,000 m. Such ordnance further imperils the future of the low-level air-support business.'
So a single gun has RoF of 450 rpm.
Here is the photo of the gun from the article (its caption indicates that the gun was by Hispano-Suiza):
And at https://projectswisstank.wordpress.com/2016/03/28/tier-5-panzer-51-mit-34-mm-hswf-doppellauf/ there is info on what apparently is a self-propelled version of the gun depicted in the Flight. It is mounted (in my opinion with no major changes) on the chassis of AMX-13 (Panzer 51 in Swiss nomenclature). The post in the blog contains also some data, incl. that the gun was being clip-fed (I would think rather it was belt-fed) and says it was developed by Hispano-Suiza and W+F Bern. The caption of the photo below confirms that - it comes from an article on the Swiss armament industry published in 2012 in the Revue Militaire Suisse (rms-001_2012_0__555_d.pdf ).
It seems to be quite an interesting gun, doesn't it?
So I wonder what ammunition it used. Was it 34x239 used in Flab Kan 38 water-cooled single 34mm gun of pre-WW2 vintage? Do you have any idea on its performance and - finally - on why the gun has never been manufactured and adopted in service?
Any info would be highly appreciated.
Thanks for posting, not seen those pics before. A paragraph from my next book (with thanks to Bob Gerber):
34 mm HSS 834 and 40 mm HSS 840: 34 x 239 and 40 x 239B ammunition.
In the early 1950s the Kriegstechnische Abteilung or KTA (Weapons Technology Section of the Swiss Defence Ministry) requested Hispano-Suiza to develop a new heavy automatic AA gun intended to replace the 34 mm Flab K 38. The resulting gun was was designed in two calibres: the HSS 834 which used an updated loading of the existing 34 mm ammunition; and the HSS 840 which used a 40 mm version of the case, with a belt added to ensure accurate headspacing. Ammunition feeding was via a linked belt or five-round clips and the cyclic rate was an impressive 450-500 rpm.
The project was shelved in the mid-1950s. Oerlikon eventually replaced the Flab K 38 with their KD series guns (see below).
At https://naboje.org/en/node/13703# there is some info on a 40x270 cartridge by Hispano-Suiza. Original Czech description may be translated as follows:
"An experimental cartridge built in Switzerland in the late 1940s, probably for an anti-aicraft cannon. During trials it developed a muzzle velocity around 1200 mps. Further information on that project remain unknown".
It's interesting that the Czech website is the only place over the Internet that contains any remark on the 40x270.
Which gun was this cartridge intended for? Was it a derivative of the HS-840 (for 40x239B) or quite a different design? Obviously its ballistic performace is interesting too.