Be careful with that nice double rifle.
Modern smokeless production loads could very likely at least damage the gun or potentially blow a barrel or worse.
Photograph the proof marks on the barrels and action flats, show us here in the thread.
There isn't a modern production load suitable for that rifle, but with a look at the proof marks, we can steer you in the right direction for getting set up to load for it.
Load data tends to be specific to the individual rifle with these nice old 19th century doubles.
What is the bore diameter?
What are the chamber measurements -- base diameter, rim diameter, diameter of chamber at the throat end..?
I own a couple of 16 bore double rifles which I've gone through and developed loads that have both of them shooting to the sights.
-Tinker
