Here is the case forming process that I prefer: The pics are from L to R
Left..................270W
second..............270 necked up to .338"
third..................338 PARTIALLY necked to .308"
last....................fire formed 300 Sherman
I run my 300 die down the neck just far enough so that there is resistance when closing the bolt (for proper head spacing)
Drop 12 grains of Red Dot shotgun powder, or equivalent, into case, fill to neck with cream of wheat, place a cotton or paper plug in neck and fire away. You can use any large rifle primer.......Rich