A standard SAAMI go gauge for the 308win measures 1.630" this figure is also known as "minimum chamber length". If memory serves me right the datum line diameter used for the 308 is .400", so it sounds like your comparator has a smaller datum diameter. This is not really an issue, it can be anything as long as you have a starting point to zero it. Since it sounds like you are just using fired vs. unfired cases to set a starting point or zero that is okay too as long as the unfired cases are right. Something has to be amiss here as you seem to have too much difference between what fired cases measure and what you have to bump them back to get the sized cases to chamber. If in fact the sized cases must have their shoulder bumped back .007-.008" to be able to chamber AND IT REALLY IS THE SHOULDER THAT WAS STOPPING IT then you have an excessive headspace problem and need the rifle checked by a competent gunsmith. If this is the case do not shoot it, that rifle should not be considered safe.
If you have to resize the fired cases so much that it takes .007" bump to get the case sides small enough to fit, then again, you have a chamber problem. Let me ask this...standard dies wont bump a shoulder back that much unless the shell holder or the die itself has been modified to do so. Have you modified either one??? If not then how can you be "bumping" back further than what a standard resize die will bump??? There is something definitely amiss here, if a small base die will size a case to fit then you have to have either a small chamber or a bad full length resize die.
Definitely have that headspace checked.
