Grenadier,

AFAIK
Jim Corbett's guns were auctioned in Nyeri Kenya after he left for Happy Hunting Grounds along with skins and trophies of man eaters he shot.

Jim Corbett had
.450/400 Jeffery (I think in Keith Elmer collection)
.500 BPE underlever by Manton &Co (Not sure)
.275 Made by Westley Richards (He shot one Man eater with it)
The Martini mentioned would most probably will be a .450 because it was a Military cartridge then rifle were very common
12 bore and he also mentions 28 bore shotgun in one of his stories

Every now and then there are rumors in India about shotgun or a rifle for a sale that once belonged to Jim Corbett but since most of his guns were auctioned after his death,The claims are highly suspicious.

Dandy