David (motto):
I poked about a bit on the net as well, coming at it from a 20mm cartridge specs comparison angle. One site actually ID'd the Oerlikon round as also being used by the Polsten. The Hispano was a separate entity.
During the 1930's and throughout the war, quite a number of other 20mm cannons surfaced from a number of nations. Two distinct usages were quite clear: an aircraft weapon and a ground/surface based anti-aircraft weapon. From what I read, the Hispano was a very popular aircraft weapon, used outright or cloned by many nations on both sides during the war. On the other hand, the Oerlikon and Polsten seemed to be very popular as anti-aircraft weapons, particularly with Allied navies and ground forces.
I am by no means an expert on 20mm cartridges, but what I read appeared to suggest the Hispano round had somewhat better performance than the Oerlikon. One interesting ballistics site compared various 20mm rounds to the Browning .50 cal at 1000 yards. The Browning was still nicely flying along at near level at that range. The Oerlikon had dropped by about 8 feet and the Hispano was in the 6 foot range for drop.
From a performance perspective I can see why Inglis likely chose that round initially, as well as the British wanting to use it in the Inglis design for that reason. Maybe what changed British thinking and doomed the Inglis gun was the desire to keep the Hispano round an aircraft item. Since most of their Army and Navy 20mm stuff was already Oerlikon, they wanted to keep it that way with the Inglis.
Eagerly awaiting Roger's book for further enlightenment.
The 'other' David
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