The Mini may have been doing it slowly for some time. My browning 1885 falling block started doing same thing. Only can't pull the firing pen on it. May try ultrasound.
I was getting light primer strikes. After some looking into. I found the firing pen inside the bolt had some kind of build up on it.
I never take the bolt apart for cleaning. Not sure what it was. It looked like it had been like this for some time.
Is this common?
I needed horns for my black powder shooter. I found finding a horn was a chore. After some testing the way old timers did it, I came up with this. The boiling the horn and the smell it gave off in the kitchen tested me and my wife being married.