I have never shot pyro of any type. I have only used goex in ffg and t7 in both 3f and 2f. Back when app was clean shot I got excellent accuracy in my old 50cal tc hawken and my old mk85 which both have stolen ,but that is another story. I have wondered about pyro. what granulation for what purposes? any comments would be appreciated. thanks

Pyrodex RS is a good powder for roundball or sabot. If shooting conicals I like the Pyrodex P. Also Pyrodex P shoots well in traditional and inline rifles for roundball and sabot. Pyrodex is messy, coorosiveand fowls a lot but it is a very consistent powder. If I do not shoot Goex, I normally shoot pyrodex. For cost and consistency reasons...

What is the difference between Pyro P, RS and Select?

Pyrodex P is a fffg equivalent, R/S an ffg equivalent, and Select is supposedly more uniform in size, but from what I've read very little improvement in actual accuracy.
I use R/S in my inlines for a hunting load behind sabots with good results.

Wabi is right on the money there. Pyrodex P is for pistol. Meaning it is a 3f grade of powder. RS is for rifle and shotgun. So it is a 2f grade powder. Select is nothing more then RS run through a screen a few more times to make it more uniform. I really used to shoot select until the store ran out once and I bought some RS. Never noticed the difference in the two powders.

Actually in my inline rifles I like the Pyrodex P for a lot of things. It seems to shoot very well and is a about 10-15% stronger in power then the RS they claim. I never ran it over a chronograph so I will not swear to it.