The difference you're seeing between the fired rounds and unfired rounds are from being fired. When fired the brass expands some to reduce rearward movement but the case still comes rearward under a lot of pressure with quite some force against the bolt face. This is most likely the cause of the difference in appearance of a deeper firing pin strike and some appearance of flattening.
Buy a box of fresh ammo and take a trip to the range. I'm fairly certain you'll be pleasantly surprised.
Heck you're gonna need it sooner or later anyway.