Roger, if you don't even know what FG means, I'd say that your safest bet, at this point is to load those gas checked bullets with just about ANY of the smokeless loads that DW put up.
SAVE delving into the mysteries of loading proper black powder ammunition for another time, and (if that Marlin Guide gun's ported) for a different rifle.
That blue lubricant has not performed WAS with BP, in my experience.
If the starting loads show great accuracy, ....just STAY there,....at the lowest Smokeless vels shown, that bullet will kill like the wrath of God.
GTC
Thanks, not going to mess with black powder.
