I've used Unique for blowing .308 cases out to 7.65x53. Bullseye worked better, but Unique was okay.
Some people use cornmeal or other filler on top of the powder. I used cotton balls, which worked okay.
Do one or two cases and see how they form. If they don't form out all the way you'll have to add more/faster powder or more cornmeal or cotton.
Generally fireforming won't give you a crisp shoulder on the case; depending on how thick the brass is at the shoulder area, it may take a couple of full-power firings to get a perfect shape.
Watch the case mouth thickness; depending on what you're forming, the mouth can be thicker than specified for the cartridge.