the australian made 303 conversions were taken from the surplus market very early by a japanese submarine in WW 2.

the existing mannlicher rifles were rechambered by ex dutch india in the 1950s to deal with 3 problems:
1.worn barrels because of the tropical climate there
2.not enough 6,5x53R ammo
3.and an offer by ex british india for WW 2 surplus 303 ammo that was to good to let it go