Cartridge Datum Length Variance

[angrygopher]

I'm wondering how much datum length variance I should be seeing. Using a Hornady case comparator and a digital calliper I observed the following measurements...
1.6225
1.6265
1.6230
1.6270
1.6235
1.6260
1.6260
1.6255
1.6250
1.6270
1.6255

I want to bump size and it seems the datum length variance is more than what I had planned bumping the case neck (.003?).

The cases are Hornady 7mm-08 Remington.

 

[bigedp51]

Are these brand new unfired cases?

Are these once fired cases from a workup load and why the different lengths?

Full length resizing will squeeze the shoulder forward and possibly make them more uniform.

 

[angrygopher]

All once fired from the same rifle from work up loads. I had expected to see smaller datum length changes.

 

[Chilly807]

In my experience, until the cases fully stretch to fill the chamber they won't be uniform in length.

Light to moderate loads may take 3 or more firings to get to this point.

You can "stretch" them by using the press with a FL die.

 

[just having some fun]

just having more or less lube on the spindle / inside if the neck can effect the shoulder

Checking the shoulder on brass on a work up load will show length difference

if you are not caming over on your press .. spring back/ clearance of the linkage can effect shoulder

Redding has shell holder set that a allows you to cam over and still add to the length ie plus .002/ .004 .006 etc