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