Why is my brass shrinking?

[BeefyT11]

Shooting a 6.5 creedmoor, full length sizing and annealing after every firing. Shoulder bump is 1 to 1.5 thou. I trimmed to trim to length after first firing and havent touched it since. Now I'm on my fourth firing and my cases are 3 thou shorter than it was 3 firings ago. What might be causing this?

 

[mikecr]

Your cases fire formed by around the 3rd round. Your necks were pulling back as shoulders took their form. Normal & not a problem.

 

[BeefyT11]

Your cases fire formed by around the 3rd round. Your necks were pulling back as shoulders took their form. Normal & not a problem.

Awesome thank you

 

[243winxb]

On firing light to midrange loads, the case body expands outward. The trim length gets shorter and the head to datum measurement also.

Your fl die would seem to be a good match to your rifles chamber, not over working the brass on sizing.

Its common for the fired trim length to get longer after fl sizing, but not always.

When brass is trimmed back .010" from maximum, it takes a while till it growes back to maximum.

 

[NorCalMikie]

Your cases fire formed by around the 3rd round. Your necks were pulling back as shoulders took their form. Normal & not a problem.

That's a good reason NOT to be in a hurry when it comes to case trimming. AND, most chambers are cut close to .020" longer than the Max trim length.
Measure the "actual length" of your chamber, write that measurement down and refer to it BEFORE you even think about trimming.

 

[Richard Coody]

Shooting a 6.5 creedmoor, full length sizing and annealing after every firing. Shoulder bump is 1 to 1.5 thou. I trimmed to trim to length after first firing and havent touched it since. Now I'm on my fourth firing and my cases are 3 thou shorter than it was 3 firings ago. What might be causing this?

Common mistake. Trimming new brass. I did it once long ago and wondered why my brass was short after firing. That was long before we had great sources of information like this forum. Now i only trim when brass gets to the max and then only trim about half that recommended length. Certainly don't trim often.

Might want to check that base to shoulder datum length on a fired case.

If you set up your shoulder bump before the cases were fully fireformed you might be oversizing your brass.

 

[Coyotefurharvester]

All good advice.

 

[ebb]

Are you telling me that the 6.5 creedmoor is so well designed and superior to all others that you don't even have to trim the brass??????

 

[kneedtospeed]

 

[theallcineyes]

Well I'm have the same issue. I now have a 50 rnd count and growing 1.895..I have not touched a trimmer to these. Been reloading awhile have never had this issue either. I'm clueless. Will tell you that changing to all peterson which I'm not having this issue. Can't wait to hear why could be happening.

 

[Earnhardt]

Why is my ass shrinking?...

Because I was born with a rare genetic defect called Assless-itis..

The only known cure... suspenders.

Great thread man!