The cream of wheat or cornmeal method will fireform using fast burning pistol powder to the 95% point IF you carefully work the load up one at a time and test it before doing all of them. You want to use enough powder to get a clean sharp shoulder. Only way is to test and shoot one piece of brass until you get there and then test virgin piece to compare.
Be sure to use either wax or tissue paper in the end of the case.
If you have muzzle brake
take it off!!!!
Second best method is the false shoulder method. Expand the necks up one caliber and then use a neck bushing to size just enough of the neck down that the bolt closes just a little tight and shoot them. Use the cheapest bullet around, and forget load testing but it puts 200 rds down the barrel which will be a lot in that case configuration. I would not use this method or the jamming into the lands.
Jamming into the lands burns the barrel the same as the false shoulder method and is inconsistent at times with ignition and final case forming.
Based on you having 200 cases to do, I would use the COW method above and try it to final fireform