4350 is a bit slow for a .308 with most bullet weights and barrel lengths.
TAC, AA2520, H/IMR4895, Varget, RE-15, N140, N150, N550 are the range you want to be looking at... and the middle two (Varget, RE-15) are almost guaranteed to work like a champ for you.
I've heard limited accounts of an individula using H4350 behind a 250gr SMK (when they used to make such a beast) years ago. They also used Remington UBR brass (mondo capacity) to be able to fit enough in the case to be useful.
YMMV,
Monte
