I know FFG is more coarse than FFFG, and have heard you us FFFG in pistols, but can it be used in long guns too?

I just picked upa pound ofPyrodex RS which I know I can use in my MZ, but they have a ton more Pyrodex P which I'm not sure about. With the sale that's going on now, I was able to get it for just over $10. Thought that was a pretty good deal, with them to only be getting better.

Thanks.