In the round ball era of the 1850's and 60's - the 16 bore was considered by many to be the minimum for tiger, elephant (India) and buffalo, this, according to Lt. James Forsyth's The Sporting Rifle And Its Projectiles, printed in 1862.

The 14 bore SXS or single, was the ultimate for these animals for the hunter to carry himself.

With the change to ctg. guns using conical bullets that could be hardened, the breech loaders surpassed the 16 to 8 bore round ball guns that were previously favoured for India, as hard balls could be used in them and out penetrated the soft lead conicals (necessary to take the rifling) of the day.

I dare say, this 16 bore was quite capable of 'taking' elephant of either country due to it's huge powder charge and hardened concial that would work in 27" of twist.

Note also, back in the mid to late 1800's, many English gun makers though MORE twist made the gun shoot harder, with many round balls guns have 36" rates of twist. They simply did not shoot well, due to 'stripping' with any big game charge.