WW1 British 2pdr modified to semi-rimmed

[Vasco Da Gama]

Came across this interesting little case and would value your thoughts on what it may be. I think it started life as a 2pdr Mk1, made in 1918 by Vickers. At some point it has been cut down to 99.2mm, the thickness of the metal at the mouth gives this away. I purchased it because of the base, which appears to be very professionally modified into semi-rimmed or close to rimless. My thoughts turned to a sub-calibre round of some sort or an impulse cartridge for some device. It came without a primer so no help there, pictured against a stand WW1 2pdr case. Over to you!
Rim is 44.8mm (2pdr 48.06), thickness 1.8mm (2.19), groove 1.5mm wide and mouth 40.28mm.

 

[BMG50]

Cant remember if these cut down cases were used for launching depth charges or was it another calibre.