I have 2 different rifles I cut specifically for a suppressor one is a 308 one is a 243. They are both threaded 1/2x28 and I run adapters on both. I feel a 20” balances well but haven’t tried shorter. The 308 crosses the chrono with a 165 gamechanger, rl15, and lapua brass at 2775. Haven’t checked the 243 yet as I am still playing with some loads.

I am thinking of trying a 783 HB in 6.5 creed for grins and they come with a 16.5” barrel.