I have loaded & use(d) three different "Ackley" cartridges, one of which was the .243AI, I shot it out & re-barreled to 6mmAI & my father shoots a 6.5-06AI.
Fire forming brass is not hard by any means, in the .243 & 6mm variants I use the seat long & jam method, we use the cornmeal method for the 6.5. I think you get a better shoulder by jamming but both work quite well. I have actually been pretty luck & had decent accuracy in the 6mm by basically throwing a load together. Great way (IMHO) to do your break-in (if you believe in that phuey), plink some sod-poodles, or just get used to your set-up.
I was in the same predicament as you when I started, I called the Sierra Bullets tech line & talked with Robert Treece (sp), great people to work with over there. He recommended the load long & jam method with a near max load (as pressure will drop when the case blows out), I've fire formed hundreds of rounds with this method w/o any hiccups whatsoever.
