Some specifications taken from an old manual from my training days at School of Artillery: "Weapons and Equipment, East European and Communist Armies, Volume II":

20mm automatic antiaircraft gun M30
20mm automatic antiaircraft gun M38
20mm automatic antiaircraft gun M38V
20mm automatic antiaircraft gun M-55

A great variety of 20mm automatic antiaircraft guns are used in Yugoslavia, but the standard weapon is a Swiss-design gun produced under license 1n Yugoslavia. However, a large number of German World War II 20mm weapons are still in use.

The German weapons are all of the M30 and M38 series which are ballistically identical. Some are C/30 single and twin naval guns, which today are primarily found in coastal defense and home defense rotes. In addition there are the single M30 and M38 and the quad M38V which are mounted on mobile carriages. These weapons may all be found with or without shields. All of the German 20mm-guns are recoil operated and are horizontally fed by 20-round magazines. The mobile guns are transported on special two-wheel trailers and placed on three firing jacks in firing position. The naval-type weapons are placed on pedestal mounts which have limited mobility.

The 20mm automatic gun M-55 consists of three Hispano-Suiza HSS 804 guns on the HSS 630-3 towed carriage. The M-55 is also used aboard warships replacing the German 20mm guns. The ammunition, however, is not interchangeable with that of the German weapons.