Never heard of it myself, but I do have a number of cases that have been made up by cutting short the .303 british case. I have a number of different lengths, one lot sourced from the derelect home of an ex small arms fitter from the Lithgow Small Arms Factory, the second lot via a third party from some hundreds of kilometers further west. They are approximately .40 to .43 calibre and loaded with a variety of cast projectiles and shot loads. I have always assumed they were a homegrown modification to suit the Lee-Enfields that were bored out to .410 shotguns, but they could I suppose be the round you are refering to.

For many years the old enfields or the martini was about all that was available for centrefire here, and the .303 british was modified both up and down, with .22 (3 different versions at least), .25, .243, .270, .35, .375 and at least one larger calibre being made up.
The .303-25 was considered THE roo gun for many years, with the bigger calibres being ozie "big game" rounds.

Roo's are not realy dangerous (unless you are VERY unlucky), and are usualy shot in the open at some distance, or over lights at night, or both, so flat shooting small calibres are the go. Skins were the main product, so damage was to be avoided.

How times change, game must be much tougher today, or perhaps we don't "hunt" as well as we did.

Last minute thought, one of the ozzie manufacturers used a kangaroo in the headstamp (Super Cartridge Co., later bought by Winchester to form WW Super), and the Martini has a Kangaroo on the reciever, so maybe that has influenced the name you were given.