Yup, shooting mine since 1986 with 3Fg. Out at the longer range I used to load up with 80gr, but modern Swiss powder will probably make the velocity and distance with 70gr. You'll notice that Capandball on Youtube uses just 60gr for HIS Pedersoli version, but leaves out the brand name...mind you, he's only shooting out to 300m.
I have a lot of Whitworth lore, mainly culled over the years from people who shoot real and replica Whitworth-style rifles. Do a search - there is a LOT! What is your rifle make? If it should be a Parker-Hale, then David Minshall here [or I] would appreciate knowing it.
We are all nosy here, and like to know a little it about new posters, so a little enlightenment would be much appreciated. I'm guessing from your syntax that you are in UK - like me?
Welcome, BTW!!