Salvaging Ammo Parts and Age

[Parashooter]

I only see reference to cases having a bullet in the mix. I do not see any reference on that forum that shows evidence that a primer in a case with no barrel restrictions can cause shoulder setback. OR I'm just missing it. Can you point me to the data to support primer force set-back with no restriction in the case mouth or chamber?

Author of post describes test with inert primers vs. live primers - no mention of bullet or powder for the test (which certainly wouldn't add much with inert primers) -

There have been basically the two theories regarding the cause; the firing pin blow theory and the primer theory. I ran the same tests with a fire formed case and inert primers; headspace was not changed. I then used the same fire formed case with live primers. In as little as two firings there was a measurable decrease in headspace. After five live primers the fired primer was noticeably backed out after firing. NOTE: this increase in headspace was with case taking LR primers.

If you really doubt that the effect occurs, this kind of test is something you can easily reproduce at home (just the live primer part needed). Cost is only a little labor and a few primers. Results vary depending on case/chamber surface condition, presence of lubricant, brass hardness, etc.