RE: roundball loads
I think that rifle resembles the old CVA rifle that a buddy had back in the 70s...
1-66 is the right twist for round balls, so don't waste your time with anything else....Its also button rifled, so it will be about .006 deep...You're probably going to do best with a pretty tight ball/patch combo...
I can't remember the barrel thickness, but I'm betting it's either 15/16th or an inch, which means, do not put more than 100grs of Pyrodex or Goex in it...With the design of the stock, you probably will stop at 75-80grs, because of recoil....The drop of the butt plus the cresent moon design doesn't help absorb recoil...
When shooting that gun be sure to put the butt plate on your upper arm, not shoulder, those guns were actually designed to be shot off hand or standing up, braced against a tree....If you actually sand bag and bend at the waist as some of us do with modern rifes it seems to double the recoil...So, if you shoot from a bench, set up so that you are sitting straight up, not crouching behind the gun....
As already mentioned 70-75 grs of powder is plenty for that gun to kill deer and 45-55 grs would be about right for target shooting....