bigcountry,

You are right on - on my powder scales - 3 pellets of 50 grain t7 on the average weighs out to 121.6 grains of loose.

I really think that t7 is cleaner than either pyro or BP, either pryro or t7 is less corrosive than BP. But I don't kow that I can say t7 is less corrosive than pyro - but definitely cleaner and over a chrono seems to have less load variations in velocity.