Generally speaking, FFFg is for handguns, and FFg is for rifles. That said, there are guys over on the MuzzleLoadingForum who use FFFg for everything. Some use it both in the barrel and the pan in their flintlocks. So it will work in your inline. Can't help you with a load, though. It'll be a bit faster burning than FFg, so I'd lower your starting load a bit and work up.