As has been mentioned, the Howdah pistol was designed for self defense at very close ranges. I believe an average distance from the hunter to the ground was about 20 feet or less, assuming the hunter is standing on the platform/basket (howdah) shooting down at the tiger before the animal has jumped upwards onto the elephant's head, trying to get to the elephant handler.
NOW if you're Mad Max, or if you lived where it was illegal to have a breech loading handgun for self-defence in your home, as it once was in Washington DC..., it might be just the ticket. Though I'd probably try to swap out the nipples for sealed adaptors that would use modern primers, if it was for home SD...,
One quote about the pistol during the age of tiger hunting in India reads, "...
to be effective [with the Howdah pistol],
the muzzle must be placed close to the tiger’s head, and care must be taken not to kill the mahout [the elephant handler].” YEAH you're a foot or two from several hundred pounds of teeth and claws covered in orange and black fur, that's pissed-off and might even be already wounded...and you need to take careful aim....
While true Howdahs were first produced as caplocks, they eventually moved into breech loading cartridges including the .476 Enfield ( with a punny 18 grain black powder load) and the .577 Snider. Apparently the cartridges in closed breech pistols with barrels longer than revolvers, gave a bit better performance than British revolvers of the day. (Pedersoli now offers a .410/.45 Colt version) Back in the day improving the performance of British pistol cartridges would be good, since the .476 Enfield was interchangable with the .455 Webley cartridge, and the .455 Webly from a revolver of the era launches a 265 grain lead projectile at about 600-750 fps. Not really what you'd want when facing a tiger, up close and personal.
The .577 Snider from a rifle delivers a 450-480 grain lead bullet at about 1300 fps, but that's from a 36" barrel, while a Howdah chambered in the same cartridge probably had a barrel 1/3 that length. Still it would be better to deliver 450 grains of lead at about 700-900 fps, than 265 grains using the .476 Enfield.
However, as late as 1875 a caplock SxS Howdah pistol in 16 gauge was made as a presentation piece for a royal tour of India, and perhaps it was more than a mere gift. Lancaster made double and quad cartridge pistols for British officers up to and through the 2nd Boer War, of the first decade of the 20th century. So there was probably something to the idea the pistol cartridges did better from a breech loader instead of the revolver.
An online article did a test on a caplock Howdah in 16 gauge, having a manufacture dated to 1825, with 7½" barrels. A 410 grain, .648 caliber ball was fired with a .018 patch, and at 50 grains of 2Fg, the muzzle velocity was 719 fps. Not too shabby, though with the added 4½" from the Pedersoli Howdah, shooting a .600, 325 grain ball, you'd likely get much better MV.
The author wrote,
"...shooting the pistol can only be described as 'brutal' - my knuckles were bruised, and my wrists felt like they were hit with a bat. ..., The accuracy of the pistol was at best modest, particularly as its light weight and heavy ball made it hard to control, and the off-center kick moved the impact point a good eight inches to the side which was fired."
http://www.ctmuzzleloaders.com/antique_guns/purdey_howdah/howdah.html
No telling what a 20 gauge would do to you.
In my state, hunting deer with a muzzle loading handgun, one must use a minimum of 40 grains of powder. The Pedersoli Howdah in .58, which is rifled at 1:24, would probably be very good on a deer at 25 yards. The 20 gauge with say 55 grains of powder and 3/4 of an ounce of birdshot might be OK for chukkar or quail when hunting with a dog so you could cock the piece prior to flushing the birds. The breech loading, .410/.45 Colt version from Pedersoli is rifled..., so would suck using a .410 shell with a load of birdshot (imho).
LD