I would have a qualified gunsmith check this Parker over carefully first. If you don't mind telling us where you live, chances are good some of the PGCA members can recommend a good double gunsmith. He will check for "on face" and minimum barrel wall thickness, any dents or damage to the barrels or ribs- And my guess is- if it passes that inspection he will recommend low pressure black powder or equivalent loads.
We are very lucky in that we have specialized ammunition companies that cater to our love of careful shooting these old treasures- RST, New Era and perhaps others- We also have many members who have spent a lot of time and study in working up reloads for older Parkers.
Do I see a hint that you might end up keeping this fine older Parker? Perhaps shooting it? If so, please join the PGCA- so much to learn and we are fortunate to have a membership that enjoys passing along such knowledge--I have learned a great deal since I joined, and also have learned that there is far more to learn--someone is always trying a new approach-
