First time ever I've had this happen. I was shooting my reloaded 350 ammo today using a charge of 24 gr of LilGun and a Speer 180 bullet with CCI 400 Small rifle primers. (charge was well below max)
I have a system for reloading where when I weigh and charge a case I move the funnel to the next case. After all cases are charged I visually inspect each case for powder level prior to seating bullets.
After shooting I noticed one of the cases did not have a primer in it and a visual inspection showed a ding on the case head from the ejector pin on the rifle. There was no obvious indication of a problem when shooting. All shots sounded the same and recoil wasn't any different.
The only thing I can figure is that the case had an enlarged primer pocket. But why the mark on the case head?
There was no damage to the rifle as it shot accurately through the entire session.

maybe show a picture of the case/ding and what rifle was this in as well??
could the ding been from being ejected oddly as maybe there was some hang up on firing pin on primer or due to the primer being out of case from impact of primer and it leaving case

hard to say without see case damage , and even then might be a guess ?

I threw the case mrbb. I do remember when I was priming the cases (I use a hand primer) that one of them went in really easy. On hind sight I guess I should have tossed it then. Lesson learned,

did you find the primer? check your Magwell, if it is pierced that lil piece of primer is most probably inside your bolt and will cause problems down the road.
RR

I did find the primer. It was setting on top of the magazine and had nice round edges so there wasn't any excessive pressure. Now these where once fired cases from factory ammo and thinking about it the extractor mark could have been from being fired in may AR 350 Legend.
There is another possibility in that there may have been a small pistol primer stuck in my hand primer when put the tray of small rifle primers in it. But the only difference between the two is that the pistol primer has a thinner cup to get a proper strike.
I guess this is one of those things that can never be solved.