That's a very nice rifle and scope. From the address on the side, it may be a cast action and should have a reversable firing pin (rim fire to center fire).

Regarding the amount of FG, black powder, if your shooting fixed, you fill the case to the bottom of the bullet at the overall length that it will chamber and touch the rifling, for a starting point.

For breech seating, you load the case full, to the top and hold it in with a wad. There are many kinds of wads but, if you don't have any, you can just use a smear of bullet lube to hold the powder in the case so it doesn't spill when chambering.

A note about the BP, I've only used GOEX powder, there are a number of other powders out there and the granulation may need to be different for best results when using them. Others can speak, regarding that.

Frank