Stumpkillers description is very good, however I would load a third load, double ball or double charge, ie: for a 20 bore, I'd load 160gr.2F and 1 ball or 80gr. and 2 balls, with 200gr.2F and 1 ball for the 12 bore or 100gr. and 2 balls, etc. After shooting,as well as before, the barrels must be unbreeched to check fit and condition. Keep in mind for evermore, you are shooting anoriginal, that's perhaps 200years old, and poorly looked after as many were, from 1900 onwards.
: These loads will easily be "taken" by any gun in reasonable condition. They must be measured before and after firing, not merely looked at. By measuring, I mean width and depth of barrel at the breech, over the threads, over the powder chamber area, etc., on marker-ink(magic marker)marks so the same measurements can be repeated after the shooting tests.
: Any deep pits inside are reason to fore-go any shooting. Deep pits are common in Damascus barrels, and in time, will come out the side of a seemingly fine condition barrel. I've sen this twice out of the last three barrels recently inspected. They looked fine, except for a couple holes that went right though. Near the muzzles, they aren't dangerous, but at the breech, they are. That's why one needs to SEE themselves. Dental pics are very good at searching out holes. It is amazing how many small pitts on the oustide, actually go right through, but it's evident if fired.
