clatrans - I would take a new, unfired case and neck it up to .308 calibre on an '06 or .308 die, or any other die in that calibre, ie: .300 mag. whatever. You only have to open it up with the expander button, not FL size it.

Then, in your 6.5 dies, size the neck down only until the case will chamber with 'feel' on the bolt, ie: what is called a crush fit. You should see a slight false shoulder on that case before it's chambered, that is, if it has excessive headspace. That is what is meant by making them fit via handloading.

Another way of seeing if it has excessive headspace, is firing an empty case with a live primer in it. The pin will shove the case forward to engage the shoulder, then the primer will back out against the bolt. The amount (thousandths of in inch) it remains backed out, will "roughly" show the headspace.

If the case is properly fitted before fireing it will not stretch lengthwise at the web when it is fireformed. It will simply move the whole shoulder foreward to where it should be. That is, if the chamber has excessive headspace.

Overly large diameter expansion at the web is caused by an oversized chamber, not by excessive pressure nor excessive headspace. You must find out first, what the problem is - oversize chamber at the head, or a bonified headspace problem.

Could it possibly be a 6.5x55?.