I just went through this with my new 6 X 47 Lapua. After prepping the cases, sizing from 6.5 to 6 mm and trimming the neck to -.002 to the chamber, I seated a bullet where I knew it was long. Chambered the round (no primer or powder of course) Ejected the round and measured how far the bullet set back further in the case. Now keep in mind, I was lucky in the fact that the bullet didn't stick in the riflings and made it easy to check after I ejected the case and bullet. I measured this, and seated a new bullet in a fresh case to +.005 to what the bullet measured, chambered and ejected and saw just a small mark where each one of the riflings touched. I started seating the bullet back in .001 increments until there was no markings from the riflings and recorded that number for that bullet. I repeated this process for each different style and weight of bullet I used. Now for the next few hundred rounds, it's easy to set the bullet wherever I want, mine prefers about a .005 jump from the riflings. Some may say I got too in depth, but I know exactly where each bullet needs to be seated to touch the riflings. You will have to repeat this process as the throat starts to erode on your barrel. Good luck and hope this helps.