This formula has been around for quite a while. I think Seyfried probably did develop it, but I don't know for sure.

No, the formula is specifically for 4198, so it would not apply to any other propellant.

The only reference I can remember Seyfried making to the claim that polyester filler has been responsible for ringing chambers was awhile back. As I recall, he said that this was probably due to using far too little of it, if indeed the filler had anything to do with it at all. He stresses that enough should be used to insure some compression when the bullet is seated. Seyfried has indicated that he has never ringed a chamber and he has certainly been using polyester fiber for filler in doubles longer than anyone else I can think of. Personally, I doubt the claim. I've used it in doubles for 15 or so years myself and have never had a problem.
------------------------------