Twice. But since we don't seem to talk about it...
The first time was a guy breaking into my house. I just happened to be sitting there playing with my rifle, so it was pretty easy to hold him until the cops got there. He was armed and expressed to the cops that if I hadn't had the drop on him he'd have shot me.
The second time was a traffic altercation. The other driver was offended that I only let the person in front of him merge and didn't let him out too. He followed me for several miles to a Best Buy parking lot. He jumped out of the Beemer and came towards me in that half trot big guys do when they are approaching a fist fight. I opened my jacket and put my hand on my pistol and asked him if we were fighting. He yelled an expletive and left.
I've never shot or shot at anyone outside military service.
Technically there was a third time, but I don't count that because it was clear instantly that he was not in his house once he'd walked in and saw the gun. We called him a cab.
Only the first time were the cops involved.
There have been other minor confrontations where I was armed that didn't go any differently from when I used to be unarmed. Why should they have gone differently?