Re: Throat length ?
To many unknown factors, it will get you close but not really, for one, the clearence between where your brass neck ends verses how deep the neck was cut in the chamber. But knowing the exact freebore is for why, if the bullet has plenty of neck depth and its touching the land or where ever you want it, the freebore is about right. Unless your trying to order another reamer and you need to tell the manufacturer what freebore you want so it matches your current chamber. What is the reason your trying to fiquire your exact throat length?
Best of Luck