Caspar, so is the .577 Boxer, the .577 Trantor?

Can you tell us what the ballistics, bullet weight is supposed to be for it?

The .577 Snider is I believe 480 grs bullet and 70 grs black powder. I don't know the velocity.

The .577 Boxer is a milder cartridge.

Both were used in Howdah pistols.

That looks like a nice fun double rifle to use. In the black powder and bore rifle days, these .577s were regarded as medium game rifles!