In reality it's not as it appears.
Most of the solid head portion of the case is not touched by any sizing die.
Because you have a shell holder and its thickness plus the lead in radius or champher on the die.
Mostly one sizes the portion just above the sold head where the real case expansion takes place.
Then part of the solid head is not supported by steel of the chamber.
If it expands the primer falls out.
You can not size what your die can not reach.
And you definitely are not reaching into the solid head
1 st pic 308 factory win chamber, notice there is no support over most of the solid head portion of the case. It could be .480" here and still chamber ...only the bolt .480 diameter goes over this portion of the .470" case head. If it expands .001" or .0015 " here your primer falls out.
The expansion mainly takes place above the solid case head where brass is thin.
Next pic here are some modified dies to make 308 into 35 Rem.
The shell holder is thinned and under cut to accept the thin silver brazed carbide ring extending from the special die. All undercut to fit inside the shell holder.
NOTICE when fully in max sizing position it still does not size maybe .030" of the solid case head. So its put in a lathe collet and turned down to size, as the case rim has to be cut down anyway.
So your factory dies do not even come close to fully sizing the solid head.
Next pic, this it the home built die to fully size the whole case...notice it meets resistance where most sizing dies do their work...this ia a real full length case sizing die...the whole case solid head and all, but does not touch the shoulder and neck.
You do not do this on a reloading press, but an arbor press.
Lube and size like using a bullet sizer.
These sizing problems are a mismatch between the rifles chamber and full length die, with tolerance stack up between the two, surface finishes, etc and even differences in brass cases and their hardness. I have a bunch of different 308 dies, maybe 8, each sizes a bit different. None are small base, but one Hornady die in particular oversizes the brass, but it does not reduce the solid head dia because it can not reach it...as shown.