RE: Tough powder question....
I found a velocity difference once interchanging. It was only like 50-100fps. But I sometimes see that with different lots of Reloader 25. So I wouldn't worry about.
The story goes, I loaded some 270win when I first started loading. Well I put them away and got back out 8 years later and forgot about them. Since that time, I switched to SC. So I could compare.