Sir S. Baker preferred a smoothbore 12gauge with short barrels shooting roundballs, as his "howdahgun"...His gun weighed only 7 pounds, and his load was only of 5 drams....but very effective shooting "down the throut" shots..
However he was asked by Sir Cumming regarding a 10bore, which Baker also had experience with, and Baker stated 12 drams is ideal..
Baker stated that a 14bore or 16bore rifle with a 4 dram load would kill the heavist game around, but not sufficiently.
In "Thirteen years among wild beast of India" Sanderson states regarding 12bore rifle and the introduction of BP Express cartridges ( page 178):
" A few years ago 12-bore rifles (1.5 Oz ball) were more generally used perhaps than any others for for general shooting, but the introducton of the has led to their very general supersession for sport the the lighter class of game. I think all experienced sportsmen are agreed that 12-bores are too insignifficant for use upon heavyclass, and that they form a half-and-half weapon neither one thing or the other".