No .308 (yet), but a .223 Ultra and 17HMR. Both got the o-ring under the barrel, polished the chamber by hand in front of the TV, and set the front rest at the barrel hinge. Then it's a matter of finding what your rifle likes to be fed.
Today was one of my poorer days at the range; I was trying loads using the Lee FCD. Worse than no crimp at all; most groups were 1 1/4" to 1 1/2" at 100yds, but finally got them back to an inch with the uncrimped loads. Most days I can shoot around 3/4" at that distance, with occasional 1/2" groups; the 17 is the same. My .223 prefers fast loads and small bullets, owing to the 1:12" twist. I don't know what the .308's usually like, but if Winchester makes a "white box" load for it like they do the .223, I'd say try it.
Good luck!