Just my opinion, but I would want .313 as an absolute minimum would prefer .314 or .315. Now that's in an "out in the elements" hunting rig, in a "from the bench only" rig I'd be much less concerned with dirt and moisture in the chamber and could tolerate .312 or .313 with a little more comfort.
You have to have room for the neck to expand to release the bullet. Failure to do so will result in more accuracy/pressure "fits" than if you just left the dern things alone and ran a SAAMI neck to start with.