RE: Triple 777 vs. Pyrodex
Pyrodex P is also a great powder and shouldn't be dismissed without a try. True, it is more corrosive and has the rotten egg smell but Triple7 also requires a thorough cleaning and the smoke has quite an acrid, breath-sucking odor of it's own.
P is also cheaper, sometimes very much cheaper. It is fine grained, meters well, easier to ignite, and provides good accuracy in many rifles. There is no hard crud ring to deal with and far less chance of stuck breech plugs.
Both are good powders and you will find people that praise/curse one or the other or both. I use both.