Regardless of what conical you buy if I were you I would pick up a tube of TC Bore Butter. Even if the conical you buy is lubed. It still helps to lube the bullet when you load the bullet. I usually take some bore butter and rub it between my fingers to heat it up. Then I liberally apply the heated bore butter to the portions of the bullet that will be closest to the barrel. This is just a little extra lubrication that can make the bullet much easier to load.
Just try a couple different ones and hopefuly you will find one that shoots. You can also back the powder charge down a bit with the heavier conicals. Most guys shoot 70 or 80 grains of BP with their conicals.
It also helps alot to put a wad on top on the powder and under the conical. They are pretty cheap. And under certain situations I have seen them make all the difference in the world.
Mark your rod and be sure to seat them to the same depth every time. Push them down with some force onto the top of the powder, but do not over do it. Then mark your rod so you can seat the next one to the exact same depth.
And have fun!! Especially with your dad. I know I enjoyed shooting my dad's Renegade with him very much. He could not hit the broadside of a barn with it. But we still had a good time. Tom.