The tap is just 5/16-36 and will pay for itself in short order as you can make any number of "modified cases" with it.
I believe you're going to need some kind of a bullet comparator to actually measure to the ogive, once you extract the modified case.
(I'm aware there are various photos showing measuring the OAL to the tip of the bullet, as the name of the product implies, but this can vary considerably between bullets even from the same manufacturing run. The ogive is the part that touches the lands.)
.30-06 Springfield: 100 yrs + and still going strong