Fired Case Length Question

[wkdickinson]

I just had a new Bartlein 1:8, 6.5 Creedmoor barrel barrel installed on an old M70 Win "Match Rifle". I took it out this afternoon for the first time, to break it in and kind of see how it shoots. Also to get a read on how to set up my sizing die. I fired 25 rounds - got some copper fowling, which was not a surprise. During the break in I did shot at some targets and the accuracy was promising.

But here is my question - when I got home I measured the length of the fired cases using the the comparitor supplied with my Whidden die set to establish a shoulder "set-back". These were new (never fired) Peterson "Match" grade cases. My plan was to set the shoulder back .002", but given the measurements (see attached spreadsheet - .004" ES) I got, I am not sure how to do that.

I am not new to this game, but I've never had a rifle do this. Any idea as to why there is such a wide distributions of fired case lengths?

 

[michaeljp65]

If they all chamber again, even if some are a little bit tight, dont bump the shoulder. Give them another firing they might even up after the 2nd firing. If the longest ones are a bit tight just bump them .001"

 

[Rdlningcltchdmpr]

What happens is as the cases blow out to fit chamber some vary on first firing. The important thing is to know your longest case measurement and a new unfired Peterson case measurement. First firing my not get cases out far enough to properly adjust the die. Once you can feel resistance on closing the bolt on a twice or thrice fired case then you adjust die to move shoulder back a small bit so there is no resistance on closing. Some of the cases will measure shorter than this but as they are sized into the die the shoulder will actually be squeezed up forward to fit the proper die setting. Pm me if this is not clear enough.