Case length shrinkage ???

[Tozguy]

When using a Redding body die for the first time on some 223 cases, I measured case length before loading and after firing. It turns out that the sample of five cases shrunk in length by between .001'' and .0025''.
Even if the body die was adjusted to only the minimum necessary for smooth bolt action, I was expecting the cases to grow a bit in length not shrink. Is it me or my dial caliper that is crazy?

 

[ericskennard]

The hotter the load, the more they shrink. The softer the load, the longer they get. You would think it would be just the opposite.

 

[jo191145]

"Before loading after firing"

As you FL size a case your shrinking it in all dimensions except one. Length. The constricted brass must go somewhere and the only option is forward. Longer
After firing the brass flows out to fill the larger chamber. That extra brass has to come from somewhere. Simply draws it back in from the neck where it recently went. Shorter.
All is normal.

Measure your brass before and after FL sizing. You should see it grow in length after.

 

[Tozguy]

I see. Thanks for help. Kinda explains too why some people never have to trim case lengths.
Secondary questions, how important is it to have uniform case lengths? There is a spread of .015'' in a batch that I'm prepping (none over the limit). Should this variation 'fixed' and if so, is there a way to deliberately lengthen some cases to get them uniform in length as opposed to trimming them all back to match the shortest case?

 

[Preacher]

Shoot some of the longer cases against the shorter ones and decide for yourself if they need tweaking or not.... Normally a few 1000th in length difference won't matter much unless your playing with a full blown bench rifle and looking for that last little .001 off a group......