CBTO the same with every bullet?

[NDSwede]

If the CBTO is a certain length such as 1.750 with one type of bullet ( Speer 120 gr gold dot for example), would it be the same for another bullet such as a Hornady 123 SST?
Could you explain your thinking regardless of your answer. Thanks

[Klem]

Swede,

Across brands and types, bullets of the same weight have different shapes. Because of this, when loaded to the same COAL (base-to-tip) they will likely have different CBTO's (base-to-ogive). CBTO is predicated on the ID of the gauge you use. Where that ID comes to rest on the bullet depends on the shape of the bullet.

[37L1]

The same bullet from a different lot can have a different CBTO. I've even seen a certain manufacturer (Hornady) have more than one different CBTO from the same box!

[stef1274]

No it wouldn't. Or it could, but that would be coincidental. It is one of the reasons for wanting to measure CBTO, because same COAL may not mean same distance to lands.

[Fess]

Distance to lands is a bit tricky because the shape at the point where the ogive meets the shank will affect it somewhat. This is more an issue with secant-ogive bullets which have the ogive meeting the shank at an angle vs a tangent ogive that gently curves away. The front edge of the rifling for 6.5 Grendel starts out at a slope of 1.5° per side (when the barrel is new). If the ogive is at a greater angle, it will slide under the rifling land and the first contact will be the shank rather than somewhere on the ogive. One result is that the distance-to-lands is longer than expected.

FWIW, some rifles don't seem to like secant-ogives, and this is thought to be one of the reasons. For the Grendel, the tangent-ogive 120 SMK tends to work well in most rifles, but its secant-ogived brother, the 123 SMK is more hit-or-miss, no pun intended. Many VLD bullets and some Hornady hunting bullets have secant ogives. There has been a trend towards hybrid-ogives, which combine the tangent shape meeting the shank with the secant farther away, but Berger may have trademarked the term. Other bullets may have it but call it something else.

https://bulletin.accurateshooter.com/201...id-ogives/

[NDSwede]

Thanks everyone for responding. I understand it better. Each person added something to understanding it more.
I recently measured 100 6mm Speer 100 spbt bullets and the lengths to ogive varied 12 thousandths from shortest to longest.
Also measured some Hornady 103 ELD-X. They only varied 1 thousandth from shortest to longest.