There are a couple of things that you need to consider when using bushing. Commercial brass is thinner than military brass, so if you use calipers and measure the outside of a loaded military round, and subtract a thousand of an inch, then theoretically that is the bushing size you need for sizing the military brass (308). When you do the same measurement on commercial rounds, you will find they are smaller in diameter so you will need a smaller bushing. To be better prepared, theoretically you should have a bushing one thousand of an inch smaller than your ideal, to be able to adjust your neck tension, for each of the two sizes (commercial and military). Also, you can use a mandrel to expand the neck back out to proper bullet diameter instead of the expander ball in the die.
If you do use a mandrel, use the Imperial powdered lube to make sure the inside of the neck is lubed.