[Bart B.]

I don't think it makes much difference in how far bullets jump from the case mouth to the rifling as long as the case neck's reasonably straight and aligned with the case body. Depending on the bullet's actual shape and the angle of the rifling at its origin, different amounts of jump from zero to several thousandths can make a difference. But you'll only get valid data with each with ammo and rifle and shooter capable of shooting no worse than 1/4 MOA at 100 yards. For most folks, there's other things to do making really accurate ammo. Especially when several thousandths (a hundred in many instances; that's 1/10th inch) bullet jump to rifling with bullets having some runout on the case axis will shoot 1/4 MOA all day long in well built rifles with match grade barrels all fit to the nth degree. Good example is Federal, Hornady or Black Hills .308 Win. match ammo; it's gonna have a lot of bullet jump to rifling and not many folks load ammo accurate enough to equal it.

You can measure fairly accurate by putting a wood dowel down the rifle barrel onto a bullet that's been gently pushed into the lands then measure the distance from the muzzle to the dowel tip with a caliper's depth gauge. Then remove the bullet and measure the dowel's tip depth with the other end against the bolt face. The difference is about what the maximum over all length should be.

Besides, with rimless bottleneck cases headspacing on their shoulder, with bullets seated to maximum cartridge overall length to be a perfect fit in the chamber, they'll still jam into the rifling a few thousandths when the case shoulder's set back from firing pin impact on the primer setting the case shoulder back a few thousandths.

And whatever spread there is between the case head and shoulder dimension is will also be transferred to the point on the bullet jacket that touches the rifling.