Finding CBTO from different book OAL's

[71GTO]

I tried searching the subject for an answer before posting my question, but unfortunately the search feature has been unavailable for the best part of today.

I measure and record the max OAL and CBTO for every type projectile that I use in my bolt action 223. Usually, but not always, the max numbers I get from my chamber are longer than the listed OAL's in the different manuals that I use.
Example: 22cal .224 dia. 77gr. Sierra Match King. The maximum OAL for my chamber is 2.294", which gives me a CBTO of 1.885" when using my Honady comparator.

Using my example above, and then using the OAL of 2.260", which is listed by Sierra (and others) in their manuals for the 77gr. SMK, I would simply lower my OAL from the max of 2.294" down to 2.260" when seating the bullet. Simple enough right, but how do you determine the new CBTO? Do you just simply measure the CBTO from the new OAL of 2.260" and then load all the others to that new CBTO measurement or is there another, possibly more accurate way to get the new CBTO?

I hope that I explained my question correctly, but if I did not please feel free to ask me questions.

Thanks in advance and be safe out there, Tom

 

[higgite]

If the bullet tip moves up or down, so does the ogive. If you seat the bullet deeper, you will measure an equally shorter CBTO. If an OAL of 2.294” gave you a CBTO of 1.885”, then 2.26” OAL will give you 1.851” CBTO when measured with the same comparator.

 

[AJC1]

You would only reduce your oal to 2.260 to meet magizine requirements, if that is really your limit. The reduction in oal is directly related to your new cbto by the same amount. Old matching bullets did not have a standard flat tip so consistent measurements were not possible. Your cbto was the answer to consistant measurements.