I have a solid aluminium blue anodized cartridge that was the souveniour round for the 1982 ECCC meeting. It is a 20 x 142.4 case (209.4mm overall). Head is 28.5 mm. What is it?
HS 820/M139/Oerlikon KAD round, I guess. Also used in the Rheinmetall Rh 202 and GIAT 20M693/Vektor G1-2. It usually measures 20x139 but some loadings were made a few mm longer.
The only other 20x142 I know is for the Japanese Type 98 AA gun, but that has a fatter case.
See pic of 20x139 below (from the Ammunition Photo Gallery on my website):
Tony–Thanks for the ID. I had reached the conclusion before seeing your posting that it had to be a 20x139 KAD. I think the extra case length is accounted for by the fact that this is a solid dummy and it is machined to include the driving band as part of the neck of the dummy round.