Just looked at Hand loader Magazine talkes about the same thing. ) Your brass is worked hardened. That is why it doesn't spring back.
Your a machinist. Why when you have a unsupported rod in a lathe do you do a cut and then two "air cuts" afterwards? Unsupported metal will move away and as you do the second. and third cuts at the same setting it takes progressively less metal off. I'm done arguing with you. Pretty much everyone who has a open mind knows I am right. Even a independent poster got the.same results I said he would get.
I would get some new brass.