All good advice from above. What I have found, military brass (LC and WCC), has about a 1.0 to 1.5 grain less. But it depends on which brass you are coming from. Win brass has the most case capacity, and will give you the greatest difference. Lapua is about .5 grain less than Win brass.
Basically, use your normal load data, and reduce your max by about 1.5, and that will put you in the area. Starting loads in the 308 are generally very light, since most manuals are pretty conservative to begin with. I always look at max, and work backwards from max as my starting point.