If you are shooting a 30 caliber, the part of the bullet that is going to make contact with the lands is going to be .300" or larger. If you take measurements on different style bullets such as comparing a RN to a tangent and a secant ogive, you will get different different distances in each bullet before you reach this dimension.

overall lengths of the bullet are a bad indicator too. The spot on the bullet's ogive that meets the contact dimension will be fairly consistant if measured from the base, but comparing several bullets from the same lot will give you several thou difference in lengths. The good news is that with a seating die with the proper seater plug installed, the bullets will be seated so that the ogive to base measurement will be failry consistant although there will be differences in COL which are pretty much meaningless.