Meathead9, I have no experience with LongShot, and no data to assist you, Sorry!
You will be working sort of on your own, like I did with the Blue Dot when I first started with this caliber/cartridge. If you use this powder, Start low and work up slowly...
Hodgdon site does have some 357Sig Data which looks nice and should provide a starting place for you to play with for the 9x25Dillon with various bullet weights.
Good luck, best regards!
NRA Life Member
BASS Life Member