Ned Ludd
Silver $$ Contributor
From the OPs wording, I am thinking the question is really about seating depth, not headspace? In terms of headspace, I typically select 10 pieces of brass from a single prep at random and record all the pertinent measurements "before" and "after" re-sizing. If the die is set properly, variance for each set of 10 measurements is usually well below the precision of the calipers.
In terms of seating depth, I am typically looking for an "acceptable" CBTO range of no more than .001", with the majority of loaded rounds falling within .0005". For example: the CBTO range I used for some .308 rounds I loaded up last week with 168 Hybrids for a match was 2.2130" to 2.2125" .
To accomplish that, I set my seating dies to deliver a CBTO value at the longer end of the range on a typical stroke; in the example above that would be 2.2130". With the seating die micrometer set properly, I generally observe better than ~75-80% of the loaded rounds will measure to this longer "acceptable" CBTO range measurement with a single stroke of the press. With this approach during the course of seating 70+ rounds for a match, you might observe a small number of loaded rounds where you either seated the bullet with a little more force than the others, the neck tension might have been slightly lower, etc. Those rounds might give a CBTO measurement of 2.2125".
Only in extremely rare cases will I find the CBTO of a loaded round to be less than the lower end of the "acceptable" range (i.e. </= 2.2120" in the above example). Any such rounds are used only as foulers/sighters. You might also occasionally observe a round to be longer than the upper end of the acceptable range (i.e. >/= 2.2135" in this example). Those rounds simply receive additional "taps" in the seating die until they reach an "acceptable" CBTO measurement.
It may be argued that this approach is a needless expense of time, even though it really doesn't take that much extra effort. However, I have loaded enough rounds by this method over the years to know that if you aren't measuring every single loaded round, there is a good chance a typical seating die will deliver a CBTO range of as much as .002" to .003" (or more) during the course of loading ~70 rounds for a match. In other words, you will have a small number of rounds in every batch that are essentially as far apart in terms of seating depth as we typically use between test increments during seating depth testing (i.e. ~.003"). I personally do not find that to be acceptable and am willing to spend the extra time/effort to correct an issue that actually IS correctible. Some issues we can never fully address during the reloading process, and we have to accept certain things on faith. Seating depth is not one of those issues.
In terms of seating depth, I am typically looking for an "acceptable" CBTO range of no more than .001", with the majority of loaded rounds falling within .0005". For example: the CBTO range I used for some .308 rounds I loaded up last week with 168 Hybrids for a match was 2.2130" to 2.2125" .
To accomplish that, I set my seating dies to deliver a CBTO value at the longer end of the range on a typical stroke; in the example above that would be 2.2130". With the seating die micrometer set properly, I generally observe better than ~75-80% of the loaded rounds will measure to this longer "acceptable" CBTO range measurement with a single stroke of the press. With this approach during the course of seating 70+ rounds for a match, you might observe a small number of loaded rounds where you either seated the bullet with a little more force than the others, the neck tension might have been slightly lower, etc. Those rounds might give a CBTO measurement of 2.2125".
Only in extremely rare cases will I find the CBTO of a loaded round to be less than the lower end of the "acceptable" range (i.e. </= 2.2120" in the above example). Any such rounds are used only as foulers/sighters. You might also occasionally observe a round to be longer than the upper end of the acceptable range (i.e. >/= 2.2135" in this example). Those rounds simply receive additional "taps" in the seating die until they reach an "acceptable" CBTO measurement.
It may be argued that this approach is a needless expense of time, even though it really doesn't take that much extra effort. However, I have loaded enough rounds by this method over the years to know that if you aren't measuring every single loaded round, there is a good chance a typical seating die will deliver a CBTO range of as much as .002" to .003" (or more) during the course of loading ~70 rounds for a match. In other words, you will have a small number of rounds in every batch that are essentially as far apart in terms of seating depth as we typically use between test increments during seating depth testing (i.e. ~.003"). I personally do not find that to be acceptable and am willing to spend the extra time/effort to correct an issue that actually IS correctible. Some issues we can never fully address during the reloading process, and we have to accept certain things on faith. Seating depth is not one of those issues.
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