Seating Depth off the Lands (CBTO)
Uses your own measured "touching the lands" CBTO to compute a target seating depth.
How this works
CBTO (cartridge base to ogive) measures from the case head to the point on the bullet's ogive where it contacts the rifling — a more repeatable reference point than overall length (OAL), since OAL can vary between bullets of supposedly identical shape due to minor manufacturing variation at the tip.
Why "jump" is a deliberate choice, not a mistake
Seating a bullet with some jump (a small gap before it reaches the rifling) is a normal, often deliberately chosen setup — some rifles and bullets group best with a specific jump distance rather than zero jump ("jammed" into the lands). The OAL conversion is optional and only meaningful if you know your specific bullet's CBTO-to-OAL offset, since that offset varies by bullet shape.
Frequently asked questions
Why measure CBTO instead of overall length (OAL)?
CBTO measures to a specific point on the bullet's ogive where it contacts the rifling, which is more repeatable than OAL — tip shape can vary slightly bullet to bullet even within the same box, which throws off OAL-based measurements.
Is more jump always worse for accuracy?
Not necessarily — some rifles and bullets actually group best with a specific amount of jump rather than zero jump (seated into, or "jammed" into, the lands). It's a legitimate tuning variable, not just something to minimize.
Can I reuse someone else's touching-the-lands measurement for my rifle?
No — this measurement is specific to your exact rifle's chamber and throat, and can even vary slightly bullet to bullet within the same box. Always measure your own rifle rather than borrowing a published number.
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