What store bought ammo and grain will work the best in my Dpms Sass I've been shooting the white box 147gr Winchester and it has been all over the place to the point its making me hate my gun.
I shoot a different semi-auto, but have had pretty decent luck with the cheapy chugger Federal from Wal-mart with 150 grain soft points. Plenty accurate and works great on hogs and deer.
Run a hundred rounds through it, clean it with Wipeout, and then try several different brands and weight bullets. Most 308's like Federal Gold Match 168 grain.
I shot a bolt, 1-10 20" and it likes the hornday 178 bthp match the best,if you get into the 1-12 twist then the lighter wt. bullets may perform better. Like said the 168 may be the ticket as well.
The only way to know is ask YOUR GUN! USMC is on the right track, in that Black hills an HSM makes the more consistent ammo out there. But what a gun likes is it's own mystery.