Two best most accurate ways IMO up to .005" is to take a fireformed case that is neck sized onlyand split the neck with a dremel tool. Put the bullet in the case and close the bolt and slowly carefully remove. Measure on the ogive using a stoney point tool, not the tip. Do this for 3 bullets. You should see .002" or so consistency.

Another way is to use the stoney point OAL guage. Which is probably the most accurate. But a pain because you go to have fireformed case modified. I have checked both procedures against each other and find the split case method jammes the bullet in the rifling about .003" more than with the OAL guage. I just keep this in mind.

I have seen people try all kinds of other way by marking dowls and just trial and error with loaded ammo on if they can close the bolt. But none are accurate within .01".

A reloader needs to invest in tools.