Having reloaded for 303 for over 50 yrs and 308 for 40+ yrs i have learnt several things.
My go to work rifle is a No5. Which is a reworked black powder shooter firing 215 gn projectiles updated to 174gn projectiles being pushed by cordite. 30" barrels cut to 24.5" then 20". I tried 124gn, 135gn and 150gn projectiles with many powder combinations conclusion the 303 is not a varmint shooter. 174gn and 215gn projectiles work .The cordite flame cuts the barrels to a point that can not be corrected with other powders. and short bearing surface projectiles. In short my No5 is very good for what it was designed to do. Barrel twist comes into play with barrel length.
My Ruger Mk11 paddle stock shoots 110gn and any thing else up to 200gn vey well ( never been higher). The only down side is the mag size ( to small). The Gunsite is tinny in comparison but works the mag is larger and probably exchangable for larger ones.
Take down of the No5 Mmmmm easier than the Gunsite but chassis makers do good deeds for newer models My take is the No5 and 303 is what it is at the end of the evolution line. The 308 has more development potential with better parts supply and less quirks.