they are not NIB.
hornady has their own head stamp. also if I understand you correctly you only purchased the brass and the boxes state a bullet weight, only found in preloaded ammo. what you bought was somebodies used brass which they reboxed and sold to to your local gun store. I will agree with the assessment that one was mistakenly fired from a 30-06 and the casing fire formed out to the chamber dimensions while the other appears to have been fired from the proper chamber.
EDIT: I just re-read the original post. you say that the PPU/PRVI blows back?
stop firing at once and take it to a gun smith to verify chamber.
I will almost bet that your rifle was bored out to 30-06.
all guns lost in a tragic smelting accident.
I never said half the crap people said I did-Albert Einstein
You can't believe everything you read on the internet-Benjamin Franklin
Bean counters told me I couldn't fire a man for being in a wheelchair, did it anyway. Ramps are expensive.-Cave Johnson.