Definitely originally sold to the State of Victoria, and before the creation of the Australian Commonwealth. Early gun - before 1901, I believe.
Appears to have sold out of service markings (the opposed broad arrows). Definitely made by BSA. S/N is 4104, Victoria accession marking 4711. Can't help with what appear to me to be Japanese markings.
Agree with Douglass that you got a very nice piece there. I'd be quite pleased to run across one like it, myself. Even if 297/250 would be a PITA to load up.
Absent comrades (sound of breaking glass)