Hi - Having both hopefully some of this will help - especially with a Bergara in 6.5
my findings were in 6.5 thee longer the barrel the better 22-24 options being the most common as many re-barrelling buy an even longer barrel for speed and added precision and long range.
In my Bergara it didn't like the heavier pills the 147 Hornady's that went well in a RPR were poos in b14 HMR - But 143 were better, 143 in hornady american whitetail even better, but when i dropped to 130 game changers it became a laser.
So my case was lighter high BC bullets was better.
In 308 having a barrel back to 20" doesn't particularly suffer - then beyond that you're in lighter carry (few hundy gram's) v speed loss and ultimately reach out distance. I have a 16.5 bushpig for the tight stuff up here in the NI - the carrry weight? Well your probably better just to leave long and buy a CF stock or swap the optic to something a bit lighter.
my 2c.
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