Mate ,
I might also be inclined to fit a new set of cones, when they flame cut out over time the groups will expand, you can get them sent over from Track of the Wolf, just need to work out the threads with a thread gauge.
Is there any information in the case or on the rifle re charge? as the rifle will have been regulated for a particular ball and charge weight. As Darryl says what ever the charge for the rifle to shoot to the sights. Is the powder flask original to the rifle?
You will have a big old bunch of fun with that rifle, have you tried the shotgun barrels? and if so how does the balance feel?

Cheers

Gordon