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Discussion Starter · #1 ·
I just went through all the bullets I have in 30 cal. and used a comparator to measure the COAL of each when lightly pushed up against the lands. I measured 5 of each to get an average.
I measured them using a Hornady comparator measured from the ogive.
The Hornady bullets were all 168's, ELD Match, A-Max, and Match.
The Sierras were 165, 168, 175, 180 Sptizers, Match Kings.
The Hornady spread was 5-1/2 thousandths.
The Sierra spread was 1-1/2 thousandths.
The 180 Sierras were 1/2 thousandth almost perfect no matter how many I checked.
The 175 Sierras were barely 1 thousandth
Nosler custom competition 168's were up around 8 thousandths.
I am done with Nosler and their brass.
Thinking I'm done with Hornady maybe.
Has anyone else had the same discovery?
 

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I can tell just what's going on there as you say you're measuring COAL after touching the lands, then you say you "measured from the ogive" which is not the same as COAL, so I'm confused as to what the numbers represent.

Certainly, because a bullets OAL can have a lot of variance with any brand and I find bullet's BTO tend to be less so but less variance than that and less so with non custom quality bullets like Berger and even Sierra. I shoot a lot of Sierra's and always sort them by BTO (actually, base to seating pin contact point) to get consistent seating depths when loading as that's more important to me than jump.

I don't care for those brass as well. Typically I use Lapua or Peterson brass, but have had good results and even decent longevity with Federal brass for my .308.
 

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Discussion Starter · #3 ·
What I am saying is I am measuring "Comparative Over All Length". (COAL). By basing the measurement of COAL with average of at least 5 measured from the bullet touching the lands and getting my starting point I can then move that point of contact back into the case .005,.010,.015,.020 etc. to set my jump.
After seating I measure from the ogive not the tip to obtain my jump setting.
Sierra bullets for all practical purposes are near perfect.
Other bullets especially Nosler Custom competition bullets are up to .008 variance.
On a bullet that far out it is a total crap shoot to repeatedly seat 20 or even 50 bullets at a repeatable depth and expect anything but poor results.
On bullets as near perfect as Sierras it would be not even a concern to have my jump off by .001 over 50 rounds.
The Noslers on the other hand would have to be set back to a minimum .018 to assure nothing was closer than .010.
The Nosler "Custom Competition" bullets are being saved now for warm up loads or plinkers.
Compared to Lapua their brass is "plinker" quality too unfortunately.
If precision is what the expected result is then absolutely everything matters.
.010 at 100yds. is .100 (a tenth of an inch) at 1000yds.
 

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What I am saying is I am measuring "Comparative Over All Length". (COAL). By basing the measurement of COAL with average of at least 5 measured from the bullet touching the lands and getting my starting point I can then move that point of contact back into the case .005,.010,.015,.020 etc. to set my jump.
After seating I measure from the ogive not the tip to obtain my jump setting.
Sierra bullets for all practical purposes are near perfect.
Other bullets especially Nosler Custom competition bullets are up to .008 variance.
On a bullet that far out it is a total crap shoot to repeatedly seat 20 or even 50 bullets at a repeatable depth and expect anything but poor results.
On bullets as near perfect as Sierras it would be not even a concern to have my jump off by .001 over 50 rounds.
The Noslers on the other hand would have to be set back to a minimum .018 to assure nothing was closer than .010.
The Nosler "Custom Competition" bullets are being saved now for warm up loads or plinkers.
Compared to Lapua their brass is "plinker" quality too unfortunately.
If precision is what the expected result is then absolutely everything matters.
.010 at 100yds. is .100 (a tenth of an inch) at 1000yds.
Hmmm??? Well, there is NO direct correlation between COAL and CBTO due to the way the bullets are tipped. Turned solid bullets would have more correlation. So, your contact point at the CBTO really has nothing to do with your COAL measurement. . . . except mostly by coincidence.

Having measure and sorted many thousands of Sierra bullets for my own use, they can be very consistent, but . . . it depends on the lot. I've had some boxes of 500 that didn't really need to be sorted and others that had to be sorted into several groups.

I know some people who just sort their bullets by COAL for a consistent BC for their long distance shooting and pretty much ignore the difference in CBTO except to know where CBTO is in relation to the lands for their seating depth.
 

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Discussion Starter · #5 ·
The jump is measured from the ogive, hence the seating depth is set from the ogive.Every bullet is seated and the cartridge is measured from the base to the ogive. I dont have any concern where the tip is in the scheme of things, it is smaller in diameter and up in the barrel.

Clarify what you are talking about when you refer to:
OAL
COAL
CBTO
 

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The jump is measured from the ogive, hence the seating depth is set from the ogive.Every bullet is seated and the cartridge is measured from the base to the ogive. I dont have any concern where the tip is in the scheme of things, it is smaller in diameter and up in the barrel.

Clarify what you are talking about when you refer to:
OAL
COAL
CBTO
If there's no concern over the tip, then I was confused why you would even talk about measuring COAL . . . .but then, you changed the meaning of that acronym, huh? ¯\(ツ)

Hmmmm??? Yes, jump in measured from the ogive and a particular jump (say .020) will often have different seating depths due to chamber variations from one gun to another (as think you are aware). Not that you were trying to do this, but when one is trying to communicate a specific seating depth, it's best to state the COAL that one can calculate the seating depth and how it relates to their chamber based on their particular caliper insert.

Clarify what you are talking about when you refer to:
OAL
COAL
CBTO

OAL - Over All Length (bullet), sometimes stated as BOAL
BTO - Base to Ogive (bullet), sometimes stated as BBTO
COAL - Cartridge Over All Length
CBTO - Cartridge Bases to Ogive
 

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Discussion Starter · #7 ·
If there's no concern over the tip, then I was confused why you would even talk about measuring COAL . . . .but then, you changed the meaning of that acronym, huh? ¯\(ツ)

Hmmmm??? Yes, jump in measured from the ogive and a particular jump (say .020) will often have different seating depths due to chamber variations from one gun to another (as think you are aware). Not that you were trying to do this, but when one is trying to communicate a specific seating depth, it's best to state the COAL that one can calculate the seating depth and how it relates to their chamber based on their particular caliper insert.




OAL - Over All Length (bullet), sometimes stated as BOAL
BTO - Base to Ogive (bullet), sometimes stated as BBTO
COAL - Cartridge Over All Length
CBTO - Cartridge Bases to Ogive
This is where we are misunderstanding.
I should be referring to CBTO.
I seat all my bullets to with a few thousandths then bring them home with a micrometer seating die to all be the exact CBTO for my perfectly accurate jump measurement.
 

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I just went through all the bullets I have in 30 cal. and used a comparator to measure the COAL of each when lightly pushed up against the lands. I measured 5 of each to get an average.
I measured them using a Hornady comparator measured from the ogive.
The Hornady bullets were all 168's, ELD Match, A-Max, and Match.
The Sierras were 165, 168, 175, 180 Sptizers, Match Kings.
The Hornady spread was 5-1/2 thousandths.
The Sierra spread was 1-1/2 thousandths.
The 180 Sierras were 1/2 thousandth almost perfect no matter how many I checked.
The 175 Sierras were barely 1 thousandth
Nosler custom competition 168's were up around 8 thousandths.
I am done with Nosler and their brass.
Thinking I'm done with Hornady maybe.
Has anyone else had the same discovery?
OK. Now that I think we're understanding each other clearly (y) . . .

I do the same in that I'll take 5 measurements of touching the lands so that I know where it is. And I actually do this after every cleaning of my barrel and chamber as I like to keep track of my throat erosion. And I too use a Hornady comparator insert for this measurement.

A couple years back I got a really good deal on the purchase of some 168 and 175 Nosler CC's and sorted them according to their BTO's in groups having measurements +/- .001 (a .002 spread in each pile). As I faintly recall, yes . . . there was quite a variance from the shortest BTO's to the longest. But since I sorted them, that wasn't a big issue for me as I don't load my cartridges to touch or jam and jump is not really a big issue for me as seating depth (the distance the base of the bullet is into the case) is very important to me. The results I got with the Nosler CC's really wasn't bad, but not as good as I expected nor as good as I typically get with SMK's. So, I eventually used up all the Nosler CC's I had and don't plan to ever go back to them either.

As for the SMK's I use, I buy them by the box of 500 and I always sort them. I used to sort them by their BTO's if I found the box to have variance of more than .003 after randomly measuring ~20 from different parts of the box. Rarely, do I not have to sort the box of bullets. There has been times when a box of SMK's have had as much as .008 variance and sometimes there are a couple outliers that are even more.

I've also uses Berger bullets and find they're typically more consistent than Sierra bullets. But then, there's a price to pay for that. ;) I do like the value I get with the Sierra bullets and pretty much stick with them for my .308 as my results are good. I'm stocked up on the 169 SMK's now, having got some good preliminary results with them. There's more work to do to find out if they'll perform well at long distance. I think they'll do better than the 175's.

BTW: These days, I don't sort my bullets by BTO but sort them higher up on the ogive using a comparator insert that has the same contact point/diameter as my seating stem. This way I get very consistent seating depth, which as I said, it's way more important to me than jump.
 

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I have tried the same experiment and came to the same false conclusions about which bullets to use and buy. It really comes down to what LOT you have and tested. I've had Sierra 175s vary by as much as .012" in CBTO from a 500 count box. When sorted I had 3 distinct groups of bullets as if they came out of three separate forming dies. They all grouped very well at 800 and 1000 yards when shot in batches. When Sierra first came out with the 175 SMK I bought 3 100 round boxes and due to military duty did not get around to shooting them until 2008! They were the finest bullets I have ever gotten from Sierra with CBTOs inside of .001" and overall length differences less than .002" which is very remarkable. I have measured Berger, Hornady, Nosler, and Sierra and they have all surprised me in a good and bad way with consistency when it comes to CBTO, OAL and weight ... it very much comes down to the "Luck of the LOT" much like 22LR ammo.
 
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