the first time i noticed my m305 denting primers was 3 years ago when i was deer hunting... i was curious to see if it the round would go off if I used the same cartridge enough times...
I loaded the same round into the chamber from my mag about 20 times in a row.. the dimple seemed to get deeper every time but it did not fire..
almost a year later, while at the range, i slammed a fresh round into the chamber and "BOOM", the rifle fired...
i was pointing downrange into the backstop when i let it go, so it was no biggie, but it did scare the crap out of me.. since then i only use CCI #34 primers for my reloads..
I'm pretty sure it wasn't a raised primer as i'm very careful with my reloads.. maybe my firing pin was sticking or something.. always better to play it safe and point the rifle downrange into a backstop when racking a round into the chamber.. a good rule to follow regardless of what kind of firearm your loading.