Different Headspace Measurements on Lapua 6.5 CM

[Gbannan]

Having some difficulty understanding why one lot of my Lapua brass has a different headspace measurement than another lot.

Every lot I've ever measured of Lapua 6.5 cm is 1.5580 before bumping shoulders

Newest lot I have measures
1.5680 before bumping.

Same gun. Bumping .002

Thoughts? Thanks in advance. I just find this to be odd. Really don't wanna adjust die for this one lot.

 

[pabrousseau]

if your die is set for sizing 1.5580 why would you have to adjust for 1.5680 cases. do 1.5680 cases fit the chamber? brass formed with different dies at the factory probably accounts for the variation in h s length.

 

[pabrousseau]

no need to bump shoulders on unfired cases if they chamber easily in your rifle.

 

[Gbannan]

no need to bump shoulders on unfired cases if they chamber easily in your rifle.

They are once fired

 

[Gbannan]

if your die is set for sizing 1.5580 why would you have to adjust for 1.5680 cases. do 1.5680 cases fit the chamber? brass formed with different dies at the factory probably accounts for the variation in h s length.

Second part of your statement shed light on my concerns of hs consistency.

 

[CShooter92]

They are once fired

So you're saying that Lot 1 is fired in your rifle and has headspace of 1.558" and Lot 2 is fired in the same rifle and measures 1.568?

Something doesn't add up there.

 

[pabrousseau]

most of the time I see some variation with 1x fired cases. not fully expanded to shoulder yet. and are you depriming before taking h s measurement? good to deprime with lee decapping pin in order to get a measurement not affected by the primer. is this a bolt gun and the same load?

 

[whatsupdoc]

Are you using the same comparator.

 

[Gbannan]

most of the time I see some variation with 1x fired cases. not fully expanded to shoulder yet. and are you depriming before taking h s measurement? good to deprime with lee decapping pin in order to get a measurement not affected by the primer. is this a bolt gun and the same load?

Yes deprimed and yes bolt gun with exact load.

 

[Gbannan]

Are you using the same comparator.

Yes

 

[Gbannan]

So you're saying that Lot 1 is fired in your rifle and has headspace of 1.558" and Lot 2 is fired in the same rifle and measures 1.568?

Something doesn't add up there.

That's exactly what I'm saying. Very odd.
Wondering if I should just keep the die set to bump for the 1.558". Would it harm the brass that sized 1.568" to bump it down to match the 1.558" headspace. Bottom line I want consistency.

 

[2aBaC̶a̶]

So have you done the stripped bolt sizing test?

 

[Gbannan]

Nope

 

[pabrousseau]

if the 1.568 will chamber without resistance pushing the shoulder back to 1.558 will be detrimental to case life. to find your chamber length remove a primer and then start the primer back into its pocket. put the case in the rifle and close the bolt. now measure across the primer in the comparator. bump shoulder .002 and length should be about right.

 

[2aBaC̶a̶]

Nope

There is a video that is proving to be elusive.

Basically it's a method to find the exact measurement of your chamber and headspace.

You strip your bolt so that it falls freely from gravity. Now take a fired case that won't chamber easily and size it down in .001 incriments until you find out where it basically takes a feather to close the bolt and it falls freely like it would without a case. This is your actual chamber size and you bump it -.002 from there.


Here is the version to find your lands. It's an almost identical process. Which is the second step you should do right after you find your rifles headspace.



I have once fired brass that varies .01 and going off once fired is an educated guess.

Whenever I get a new rifle these are the first things I do before I reload.

 

[FLIGHT762]

Here it is:

 

[918v]

Having some difficulty understanding why one lot of my Lapua brass has a different headspace measurement than another lot.

Every lot I've ever measured of Lapua 6.5 cm is 1.5580 before bumping shoulders

Newest lot I have measures
1.5680 before bumping.

Same gun. Bumping .002

Thoughts? Thanks in advance. I just find this to be odd. Really don't wanna adjust die for this one lot.

Maybe your barrel unscrewed from the receiver.

 

[Gbannan]

Maybe your barrel unscrewed from the receiver.

Checked. She's tight