I don't know about doubles but I've used 777 in a 45-70 single shot. It seemed to work well, it burns cleaner than BP and doesn't foul like BP. Accuracy seemed good too. As Curl says it does seem to be more corrosive; all you need to do is not let your brass or barrel sit too long before cleaning. It cleans up real easy with a little hot water; a few patches dunked in hot water got my bore completely clean. For brass, I would dump them in a bucket of hot water to dissolve the residue. Rinse them real well, let them dry and tumble them. I did leave some in the hot soak too long (a day or two I think and they were pretty corroded).