I am currently researching cannon cartridges, 20-57 mm, and am now canvassing opinions on how to describe them. The usual method is to list the calibre and case length, with modifying letters to identify rim types other than rimless. This is so convenient for identifying different cartridges of the same calibre that it is applied retrospectively to cartridges which have never had any official metric designation, e.g. the 1.1 inch USN round can be found listed as 28x199SR.
However, once you get stuck into experimental as well as service rounds, you will find more and more examples of different cartridges with the same calibre and case length. The best example I know is 20x110; the well-known ones are 20x110RB Oerlikon S, 20x110 Hispano HS 404, and 20x110 USN (Mk 100 series). There were also some experimentals: 20x110 Scotti; 20x110 Russian AP20; and 20x110R Russian TsKBSV-75.
I have seen some instances of collectors who have tried to assist identification by adding a third measurement: the rim diameter. So the 20x110 rounds would become:
20x110x24.8 = HS 404
20x110x29.5 = USN Mk 100
20x110x21.9RB = Oerlikon S
20x110x31.0 = AP20
20x110x31.0R = TsKBSV-75
20x110x24.8 = Scotti.
This should make it much easier for collectors to identify cartridges.
You will immediately notice a problem, in that the number designations for the HS 404 and Scotti remain the same (the Scotti case has a tapered shoulder like the Oerlikon’s), so in that case “Scotti” would still need to be tagged on, but such instances are rare.
Any thoughts on this? Would it be worth doing, or is it too complicated?