The lube is to help prevent leading of the bore. It is desired when shooting full bore lead conicals.
Personally, I would stear clear of the Great Plains, just too many other good bullets out there to use those IMO. The Great Plains/Buffalo Bullets are of hollow point, hollow base construction. It just doesn't leave a lot of bullet integrity between these hollow cavities. In my testing, these bullets ring out when encountering hard mass. Pure lead bullets do not need a hollow point to expand, especially when hunting big game. Sure these bullets have worked in the past, but there is NO WAY I would be caught in the elk woods with one in my rifle.
A good solid pure lead conical without a hollow point or hollow base can be sized to the bore, load like a dream, and hit like the hammer of Thor!
777 is a very good powder for shooting full bore conicals, either the FFG or FFFG work well.