[Unclenick]

Ike666,

It is not uncommon for the end of the case mouth to be curled slightly inward and prevent a bullet being pushed in. This happens because case necks expand from the shoulder forward during firing, with the mouth letting go last. Gas starts leaking past it before pressure can expand the last little bit, equalizing the pressure. How tight the mouth remains depends on how thick or springy the brass is (number of reloads since last annealing).

SAAMI .308 drawing specifies the loaded round's neck over the bullet to be 0.3435" +0.0000/-0.008", so 0.3355" to 0.3435" would be the manufacturing limits. Lot's of folks turn another little bit off for better neck concentricity. It makes the bullet grip lighter but more consistent and centers better in a tight chamber. It has the drawback of working the brass more on each re-firing in a standard chamber, so it needs annealing more frequently to avoid neck splitting. Most benchrest shooters get special chambers with narrow necks cut for those extra thin case necks, and a standard case often can't even fit into one. That narrow chamber neck limits the brass neck expansion with each shot so it then doesn't get overworked on reloading.

Bottom line is that the SAAMI minimum is not really a safety or function requirement. A thinner neck may be more vulnerable to bending slightly off-axis running up a loading ramp, but that's mainly a concern in self-loaders or rapid fire pace bolt gun operation. You've got nothing to worry about.