During WW1 a family by the name of Bannister? bought up reject Springfield rifles from the factory most of these had brittle actions and re-heated them and converted them to .303 British but they were not a success the British rejected them but took some as drill arms about a thousand were made , maybe one of these went on safari?

I would guess it was a P-14 in .303Brit as it was standard military round in Kenya and .30/06 a bit hard to find in them days?

I see the Winchester 1895 in .405Win was popular with early safari's maybe they knew something about the .45/70 that todays shooters have forgotten!

Steve