The standard breech loading "howdah" pistol was probably a 577 double Barrelled handgun.

These 8-bore howdahs? Never heard of them? Or even a 12-bore rifled cartridge firing howdah pistol?

I think a smooth bore 12-bore howdah double barrelled pistol with a slug would be fine considering the very short ranges. As was written in another thread the trigger placement must be different to the usual shotgun action as the grip and finger reach is different on a pistol. .

Pity they are illegal in most places.