It would be best to take those pre-formed .308 jacketed cores and swage them again in a .311 core seating die. If you skip this step and then proceed to form the point the shank of the bullet will, most probably, be very slightly cone shaped, going from .311 at the heal to about .3085 at the place where the ogive starts. I know. I've gone that route thinking I could 'get by' by only buying a PF die a few thousandths above a set I already had. While the bullet 'looks good' and shoots relitively well, the shank is not parellel. I do not know what effect, over time, this would have on the barrel's throat, but I do know the bullet isn't as it should be.