Buds gun shop had a bergara barrel chambered in 300 blackout for an encore in stock.
Also, bergara makes a barrel for the CVA apex in 300 blackout. That is the one I have and it is very quiet and holds under 2" at 100 with 220 gr matchking subs.
Why a 300 whisper over 300 blackout? Blackout is more common and easier to find and essentially the same as the whisper.
Do not buy a 308 if all you plan to shoot is subs. You will be drastically limited by the twist rate and case volume. It is possible, but much easier and more efficient in a 7-8 twist blackout.
--Daniel