Thank you both for your info. I went back through my (very small) reference library and was unable to find this round. I did look before posting but I thought I may have missed it. However, I did find this on the Imperial War Museum website:
rimmed straight case with round nosed bullet. Battery cup primer.
a relatively uncommon cartridge listed by Eley Bros, and using an internally lubricated bullet. The case appears identical to the .440 Kynoch, which, however, used an externally lubricated heel type bullet. While originally a pistol round, the .430 achieved wider use in rifles for kangaroo and seals.
None of my books had the .440 Kynoch either. For some reason the IWM photos do not load. I just see a generic placeholder.
The projectile in mine is flat nosed, with tapered sides, not round nose as in their description. The picture I posted doesn’t show this very clearly though.