I agree with Azserigan. The only time I have seen this happen is when the trigger pin was walking off. Be carefuprotrusion holel at a public range. I remember reading about a fellow shooter several years ago at a public range that had his AR fire off 2 or three rounds in full auto. An ATF agent was on the range and the guy was arrested and went to jail. I don't remember the outcome but I bet his legal fees were not trivial.
I have heard of hyperextended firing pins causing a problem or crud in the firing pin protrusion hole causing a full auto condition. I once had a savage 22 semi auto rifle that would split the firing pin around every 4000 rounds and go full auto. This would usually happen after reloading and chhambering a round. I surmised that the rifle didn't like firing on an empty chamber and as a result, the firing pin would eventually split. Be very careful!
I have heard of hyperextended firing pins causing a problem or crud in the firing pin protrusion hole causing a full auto condition. I once had a savage 22 semi auto rifle that would split the firing pin around every 4000 rounds and go full auto. This would usually happen after reloading and chhambering a round. I surmised that the rifle didn't like firing on an empty chamber and as a result, the firing pin would eventually split. Be very careful!
