Here's the way I did it with my Sendero which was not making any lands marks on the bullet after blackening it with a sharpie.
Neck size a case... new is best so it fits easily in to the chamber.
Seat a bullet into the case and use a kinetic bullet puller to pop it out.
Repeat this process until the neck is streched enough that you can seat the bullet by hand and move it up and down the neck by hand, but still have some slight tension. I had to repeat about 20 times.
Then, seat the bullet a little long by hand and measure the COAL
Slowly and carefully, insert the cartridge and chamber with your bolt.
Slowly and carefully open the bolt and remove the cartridge keeping a finger on the case so it doesn't flip out.
Remove and measure the COAL.
Pull the bullet out of the neck slightly and repeat the chamber and remove/measure process several times to ensure you are getting a consistant reading.
Neck size another case and seat the bullet a little long and measure. If you have a micrometer seater the rest is easy. If not, keep seating the seater deeper until you get the correct COAL, then lock it in.
I did this with three different type of bullets and it worked like a champ.
A little time consuming, but IMO, very accurte.
Also, if you dont have a micrometer seater (get one) make a seated gauge from an uncharged, unprimed case and bullet that you can use to turn the die down on until it stops on the bullet for future seating... especially if you are working with more than one bullet.