Re: barrel length for suppressed .308?
It's your rifle it can be whatever you want it too be... there is really no "norm"
Just remember, you are adding between 7" and 8" to the length so if you are just moving from the car to the line, no big deal, but if you are gonna move with it, I would err a bit shorter.
Optimally if you wanted to cover all bases, 22" is about perfect.