Headspace issue

[AaronEdwardJames]

I have fired factory 300 grain lapua loads and once all were fired I decided to reload them myself so I checked the headspace on Redding dial indicator and it was .004 over minimum, after firing my reloads I checked headspace to see how much expansion and it has shrunk down to .0025 thousands , why has this happened?

 

[philipbrousseau]

.0015 is very little. did you deprime before measuring. any small burr on the case or primer could show that difference. as brass is fired it work hardens and spring back can change. different pressure of loads.

 

[AaronEdwardJames]

Right enough I didn't de prime when I done that , that's the problem alright,