For years I have reloaded and used the case overall length listed in the various manuals and with most guns have had good luck and decent groups.
Over the years I have tried different methods to crudely measure my chambers,but rarely went more than a .10" or two farther out than what the manuals said.
I bought a Hornady OAL gauge set and was really surprised when I measured the chambers on my Savage 25/06 and 300WM. I can go another .250-.300" on some loads and still stay off the lands .30-.40. I didn't think it would be that big a difference,but was I wrong.
This has got to be the easiest way to precisely measure the chamber of any rifle.I wish I would've bought this a long time ago.