Segregating rounds by COAL?

[nikonNUT]

I was bored... Let's just start there. :lol: I loaded up a few rounds and held the CBTO to .0005" as verified by my Zeiss Contura G2 CMM in my underground clean room... Fine, I used calipers. Anyways I held them to +/- .001 (give or take the calipers wonkiness) and then measured the COAL. Results varied as much as .010". Is this poor mans work around for using dual comparators to measure individual bullets ogive length and does it matter? Or an I just wasting my time thinking I should segregate rounds this way?

 

[PinesAndProjectiles]

What kind of bullets are you measuring? Do they have plastic tips, or are they hollow points?

I've found that measuring from bullet tip yielded major inconsistencies as the tips on some bullets vary.

Bullets with plastic tips tend to be more consistent.

Here is an example of a HPBT that has a tip that's all over the map. Look at the bullet on the right. Measuring a pile of these would be a mess.

 

[whatsupdoc]

Hey if you are that bored I have a couple of cars that could use some wax.

And I thought a $600 priming tool was over the top but now you are the king using a $65K tool to measure OAL.

 

[nikonNUT]

What kind of bullets are you measuring? Do they have plastic tips, or are they hollow points?

I've found that measuring from bullet tip yielded major inconsistencies as the tips on some bullets vary.

Bullets with plastic tips tend to be more consistent.

Here is an example of a HPBT that has a tip that's all over the map. Look at the bullet on the right. Measuring a pile of these would be a mess.

View attachment 7474830

I was measuring a few rounds loaded with 300gr Scenars. I haven't tried the 285gr ELD-Ms yet as I "asssume" there is an extra machining/forming step to uniform the bullets for the installation of the plastic tip...

Hey if you are that bored I have a couple of cars that could use some wax.

And I thought a $600 priming tool was over the top but now you are the king using a $65K tool to measure OAL.

I actually have access to one but I would probably get beaten, then shot, then beaten again for wasting it on something as trivial as a government project aka measuring hand loads... I am curious about attaching the optical scanner (probing each round would suck! Just run a macro and let the computer spit out the SPC results) and seeing the what results were....

 

[kingaling]

CBTO is better anyway as the measurement is from the base to "roughly" where the bullet makes contact with the rifling. So sorting based on an end-to-end measurement is a waste of time. IMHO.
COAL may come in to play though if they wont fit in your magazine.

 

[Steel head]

Maybe if you doing it with solids or sorted, metplated and tipped
With regular bullets it’s silly.

 

[straightshooter1]

I was bored... Let's just start there. :lol: I loaded up a few rounds and held the CBTO to .0005" as verified by my Zeiss Contura G2 CMM in my underground clean room... Fine, I used calipers. Anyways I held them to +/- .001 (give or take the calipers wonkiness) and then measured the COAL. Results varied as much as .010". Is this poor mans work around for using dual comparators to measure individual bullets ogive length and does it matter? Or an I just wasting my time thinking I should segregate rounds this way?

It's common for the length of a bullet to vary a lot and not so much the base to ogive measurement. High quality bullets, like Berger's, tend to have minimal variance in their OAL while their BTO varies little. It's the BTO that is much more important than the OAL. So, when a bullet is very uniform, so will you COAL.

When I buy a batch of bullets, I'll measure 10-20 of them for BTO to see what kind of variance is in that batch. If there's a significant difference. I'll then sort my bullets into groups having +/- .0015 (a .003 spread). Doing so give me cartridges with very consistent CBTO's. And I simply ignore the COAL except where getting them into a mag might be an issue.