I see no reason a 308 or any rifle not intended to be shot past 500 shouldnt be 16 inchs (assuming intention to suppress). I dont think id do another rifle any longer. At most your looking to gain 100-150fps going to 20 inchs. In most combos that velocity is gone in under 100yards anyway. I have never once wished my barrel was longer. And at no point would it have made a difference in a hunt that wouldnt have been easier solved by running something other than 223. In a creed sized case or more 16 inch gets you well beyond 500 if you can shoot that far.