Hello everybody,

I noticed that there was a small round dent that was no more than 1mm in diameter at the center of the percussion cap of an ejected, but unexpanded 5.56 M193 cartridge. Is that dent caused by the ejection of the cartridge by the M-16 or is it just a part of the design by the manufacturer?

Would that above mentioned cartridge still be safe for future usage or storage? If so, what are the possibilities for an unexpanded round to deteriorate and explode by itself under storage regardless of its conditions?

That is the imprint of th firing pin from when the bolt closes on a chambered round due to the free floating firing pin. Don't be afraid to go to some AR Sites to read up on the functioning of the AR series of Rifles.