If Pyrodex is all you can get, I guess we can't fault you. I would keep looking for authentic black powder as you will be much happier using it in the long run.
There are two power levels you are looking for. First, and the one you will use more often is a target and small game load. Start with 50 gr. by volume, and stick with it until you can obtain reasonable consistency with your rifle. Then move to 60, then 70 and maybe even 80 grains. I bet you will end up with about 70 grains as a target load.
The other will be a hunting load, but don't be in a hurry to burn all your powder until you can hit paper well at various ranges up to 100 yards. Once you have a load you are happy with make a powder measure to hang from your shooting bag strap.