Not a service pistol in the sense that it was issued but private owned pistols in this calibre were made and sold. Thomas Bland made one and it was reviewed in a special edition of G&A in 1995. Lancaster made a two shot over and under that is more commonly found today. You can probably google it up. The round you have is for those pistols.
Calling it a howdah pistol calibre is a misnomer but a very common one. True howdah pistols were veritable hand cannons used as the last chance between you and a messy death should the tiger try and run up the trunk of the elephant and attack you. Most of them were cut down double barreled rifles custom made They were placed in holsters at the front of the howdah to grab.
The use of the name “howdah” spread ( a bit like magnum) and is popularly tagged onto this calibre but its principle use would have been as a defense against two legged attackers. Given that the British Empire had quite a few mutinies and uprisings the risks were real enough to find comfort in a good handful of pistol. The .455 Webley service revolver did not have the stopping power that you might imagine it had by looking at it, so a bit more would be welcome should the need arise.
Despite its size its not that powerful that it would prevent a mad as heck eight foot tiger from dragging you bodily out of a howdah and chewing your tender parts