Originally Posted by phorwath
You're stepping down the neck about 0.024" (.308-.284), so one-step resizing of the neck should be no problem whatsoever. Good luck and this sounds like an interesting cartridge - which is what drew my attention to your post in the first place.
MBrown's post caused me to realize that you were planning to neck down using a Redding S-type FL sizing die with neck bushings. I had to go back and read your initial post to confirm this. I've never sized necks down a full caliber using the Redding FL neck bushing style resizing die, so you better follow MBrown's advice if that's what you're planning to do.
I was thinking you'ld be using a standard 7mm WSM FL sizing die to neck down the 300 WSM brass by setting the die depth so that it only sized the neck down - without setting the shoulder back. It would be possible to proceed as I envisioned, but it appears you would need to grind 0.200" off the bottom of the 7mm WSM die so that the 300 WSM case neck could be sized all the way down to the shoulder. Using this approach you could neck down up to ~ 0.030" in a single step. I know grinding 0.200" off the base of a 7mm WSM FL sizing die sounds crude, but I've done this before and the die is completely functional for its purpose. It just looks rough on the bottom end. If you have a lathe, then the 0.200" can be turned off in a lathe and the die will both work and look nice too. Purchasing 4 Redding neck bushings simply to size down your case neck in four small steps will cost more than purchasing a standard plain-Jane 7mm WSM FL resizing die, and will require four separate steps. Just tossing this option out there for your consideration. I wouldn't even use the expander ball if you went this way. Set the die in the press to resize the entire case neck, then use the outside neck turning expander mandrel to expand the case neck to the proper ID for outside neck turning.
Sorrry for not providing information applicable to your specified neck-down process the first time around. I don't know how far you can neck down in one step with a neck bushing style die. You better follow MBrown's method if you go that route.