As with anything, first time takes a while, but I have found the DTL for all my rifles this method for so long I can find DTL in a matter of minutes.
Here goes:
1. Clean chamber/throat.
2. Muzzle to sky with buttstock on bench.
3. Load a newly sized brass into the chamber with your pinky finger. Press hard on the back of the case head. It should fall by gravity after release.
- This is a test piece of brass to ensure there are no hang-ups/false reads with the brass to chamber fit.
4. Same piece of clean falling brass, load a bullet longer than usual by say .070" over max listed COAL.
5. Slowly insert the round into the chamber pushing very slowly with your pinky.
- Stop pushing when you feel resistance. This is the contact of the bullet with lands. (Turn off the radio, close your eyes, and snail slow to feel this)
- If you stop at the first detection softness, you can free the round with a subtle rap of buttstock on bench. If not, punch out w/rod from muzzle.
6. Seat bullet deeper by .003 and repeat until the round falls freely with gravity when you release your pinky.
- A bullet will stay in the rifling with even .001" into them. So, when it falls free, you are extremely close to the lands. Likely .001-.002"
7. Record that length with a CBTO gauge and record that COAL for that bullet until you get a CBTO gauge. You must do this for each different bullet type, weight, brand, etc.
8. You will now know how far your bullet jump is when you load. Most people seat match bullets starting .000-020 from the lands.