There is a few handy stabilizer calc’s on the Internet if you wanted to input velocity, twist, bullet weight and atmospherics. I couldn’t tell you off the top of my head how light of a bullet you would need to go in order to get a stabile sub load from 308 Win. Elevation plays a role in it, as thinner atmospheres will tolerate slower twist rates. So what works for me at 6000ft might give you trouble at Sea Level.

Trail Boss is defiantly the way I would go for light loads in a 308 Win. Be careful as you can still get yourself in trouble with Trail Boss. Do you own a Chrony?