Daniel Laws - Flattened primers do not necessarily mean over pressure. It can, but this situation can happen too... If there is excessive head space (or some times just a little), when the firing pin strikes the primer, it drives the cartridge ahead into the chamber. Then the primer goes off causing the powder to ignite. This will stick the cartridge walls to the chamber. The primer is then pushed out of the case protruding past the end of the cartridge. The case then stretches to fill the chamber (just above the web area) and it flattens the primer against the breech face. Primer signs of over pressure can be misleading. A better way is to measure the case head diameter (just above the extractor groove) before firing and then after. If it grows in diameter by a few tenths of thousands, then you have a over pressure situation. Reading over pressure signs can be a little tricky. When I fire Winchester White box 45 grain 223's in my Ultra Handi, the primers are flattened out pretty badly, but I do not have an over pressure situation. It is due to the phenomena that I just explained.