From another thread: .308 v 7.62 NATO Close, but the objective is to prevent the back end of the case breaking off from head separation. Tight headspace is the cure. Again, remember that the front of the case (shoulder) is well centered in the chamber shoulder when it fires. This is the key to bullet alignment with the bore. If you don't understand how this happens both before and when the round's fired, forget anything about where the case is behind the shoulder; it doesn't matter. On a rimless bottleneck round, the back end at the pressure ring will always be pressed against the chamber wall opposite the extractor. Any off center amount will be equal to half the diameter difference between case and chamber at that point. If a .308 Win. case diameter at the pressure ring is .4703" (SAAMI spec.) and the chamber's diameter at that point is .4714" to .4734' (SAAMI spec.), the case head center will be between .00055 and .00155" off center; always in the same direction. Which means while the case shoulder's still well centered in the chamber shoulder, the bullet tip is about half that much off center. More importantly is the fact that each and every round's set this way and they all are very repeatable in this regard. In 7.62 NATO chambers, the difference will be a thousandth or so more due to their slightly larger diameters. Bullets are pushed out of the case neck long before the neck expands. Any neck expansion will always be behind the bullet as it exits the neck anyway. It only takes a few dozen pounds of pressure to push the bullet out of the neck. By then, the bullet's already aligned with the bore. Regarding where the case head is as it's held by the extractor, note the extractor lip has enough clearance to the bolt face to easily allow the rim to fit into it when loaded from the box magazine in actions with Mauser style claw extractors as well as the push-feed post '64 Model 70 style bolts with the sliding extractor in the bolt face. There's a few thousandths clearance between the rim and the bolt face behind it and the rear of the extractor lip in front of it. Plunger style ejectors push the rimless bottleneck case forward and they stop with their shoulder against the chamber shoulder before the rim stops against the extractor's lip. Same for external claw style extractors.