C'mass,
Dixie Gun used to have suggested powder charges for various bore sizes in their catalog.
Matt Switlick also has info in his book "The Complete Cannoneer" (paraphrase).
I used to use that, double charge, and double ball it for a proof test, metal stamp the proof charge,
and date done, and normal working charge on the trunnion end.
Be in a safe position during the proof operation.
I have had carriages split during proofing so made a temperary carriage for that use.
It is good to mark a barrel because some day it may be in some one else's care.
This can save them injury, and you some liability.
You may want to start with a light load, and work up if worried about a blow up.
All this depends on the guns design, material, and workmanship.
This is my opinion, Take it, or not, is your option.
Kap Pullen