Dont do it
Hi don't do it. We fit hundreds of Palma type barrels. They have to be under .3075" some are as tight as .306".
The limited projectiles used must be under 155gr so their is only a short bearing surface st the tighter bore allows a tight seal on the projectile.
If you use heavy projectiles the tight bore creates to much back pressure causing distortian to the jacket and projectile. Any 30cal that will be shooting 190gr+ bullet weight we have found they don't shoot well at all.
However if you only want to shoot 155gr Sierra,s then a 14 twist 307 barrel would shoot verry well but you will be limited in projectiles