Why an oiled case would cause a flatened primer is beyond me,
I've never seen it, anyone else seen such a thing?.
Good luck!
i've read about some guys getting pressure signs up to and including blown primers from wet ammo (such as rain on exterior of cartridge). i've shot wet ammo less issue before, so i was curious and emailed Hornady, Federal, and two guys posting on the boards that work in ballistics labs asking why. the replies just acknowleged the issure and cautioned against using wet ammo, but i did not get a satisfactory explanation as to why.
It also increases bolt thrust. Oil, resizing lube, residual cleaning solvent in the chamber, or even water prevents the brass case from "sticking" against the microscopic (and sometimes not so microscopic) tooling marks inside the chamber left over from the chambering reamer. The case is confined in the chamber at peak pressure as if it were a brake shoe expanded against a brake drum. This reduces bolt thrust and locking lug loading during the firing cycle.
As a test Ackley removed the locking bar from a Model 94 and fired it (remotely), the bolt did not fly out or the case burst because it was held in place by case "stiction."
Fire forming an improved cartridge with too light a load will cause primers to back out appearing as if there was excessive head space. Because the case swells to fill the chamber, the primer backs out as the case shortens, and there is insufficient residual pressure to force the case backward to pick up the primer. All caused by the relationship between case stiction and pressure.
