10) Measure it with Hornady tool described in these posts or buy a similar one made by Stoney Point. It measures ogive to base of the case. Subtract 0.01, 0.015 or 0.02" from that reading and that's the length your seated rounds should be
If you have the Hornady (previously Stoney Point) OAL gauge, there is no need for all those shenanigans.
I tried the method you describe also. While it certainly gives you a general idea, when you're playing with measurements of .001 it isn't close enough. I suppose that if you're setting the bullet .010 or more of the rifling it's probably close enough but many handloaders are looking for .005 or less, maybe even "kissing" the rifling.
I tried all these methods, trying to save myself $25. It's just not worth it. Spend the $25 and get solid, accurate, repeatable results.
Still happily answering to the call-sign Peetza.
The problem, as you so eloquently put it, is choice.
He is no fool who gives what he can not keep to gain what he can not lose.
-Jim Eliott, paraphrasing Philip Henry.