In a fantasy world of unlimited funds, I'd also consider the .577 Snider. Or custom versions of the .577 NE or .500 NE. Shortened brass cases into a Howdah pistol length case.

The .500 NE .510" and .577 NE .585', Shortening brass, not a problem. Or maybe the .577 BP just loaded down.

Existing pistol or lighter weight projectiles? What true calibre are the .500 handgun cartridges? I think Woodleigh makes a lighter .577 bullet? Or did. Will look it up. Or a lead round ball load.

500 BP .510" 440gr RN SN

50 Alaskan & 50/110 Win .510" 500gr FN SN

06A 500 Nitro .510" 450gr RN SN

577 BP Express .585" 650gr RN SN
3A 577 Nitro .585" 650gr RN SN
4A .584" 650gr FMJ

Existing Double Rifle designs could be modified by the makers into a Howdah pistol. One problem, is .500 and even more so .577 rifles tend to be heavier bigger. Not ideal as a Howdah pistol. Hammers, though are desired.

With unlimited funds, anything might be possible.

I'd get it made to take a detachable butt stock. And even worse Allow it to take unobtrusive mounts for a red dot sight. Make it versatile and useful.

But if a ,577 Snider case can use a shotgun shell or brass case, it's already there and works.

Maybe I need to start a go fund me, ha ha ha.

Everyone does these days. For this intriguing project. Only joking.