CBTO measurement question

[notthattomsimonson]

I'm new to handloading and have a couple questions about the CBTO measurement. I bought the Hornady OAL gauge and bullet comparator set. Just had my Tikka rebarreled to 280 Ackley so I bought a few different bullets to try out along with a few boxes of factory ammo.

Using the Hornady tools, there was quite a bit of variation in the CBTO measurement between the bullets (I repeated the process 2 or 3 times for each bullet, these are averages):
Bullet 1: 2.68
Bullet 2: 2.70
Bullet 3: 2.77

Maybe I'm thinking about it wrong, but shouldn't the CBTO measurement be the same regardless of bullet? I thought that was the whole point of measuring to the ogive instead of looking at COAL. That 3rd bullet is a Barnes 150gr ttsx, which I know is a long bullet, but I didn't think that mattered for CBTO. Are these tools fairly inaccurate or maybe I'm not being consistent with how hard I jam the bullet into the lands? Anyone else have a similar experience?

2nd question relates to the factory loads: The CBTO measurement was 2.66, 2.70, 2.71, 2.70. If my chamber CBTO measurement (using the measurements above) is 2.70, does that mean that 3 of these 4 factory loads are going to jam into the lands when I try to chamber them? Just got my gun assembled and haven't been to the range yet to test it out, so maybe I'm just worrying about nothing?

 

[wind gypsy]

Yes, you are thinking about it wrong. People measure to the ogive because it’s a more consistent measurement than the tips of the bullet typically. It’s a better way to measure bullet distance from jam, that’s about the gist of it.

Factory ammo is generally loaded close to or under SAAMI max coal. The length of bullet noses varies widely, thus BTO measurement also varies widely.

 

[waspocrew]

Which projectiles are you measuring? 3 of the same brand/weight or 3 completely different projectiles (like Barnes, Hornady, and Berger)? The ogive will differ between brands and weights due to different projectile profiles.

 

[Pickettpuncher]

Which projectiles are you measuring? 3 of the same brand/weight or 3 completely different projectiles (like Barnes, Hornady, and Berger)? The ogive will differ between brands and weights due to different projectile profiles.

The measurement will be different with same brand and different style as well. Like the eldm vs eldx.