My late cousin was an NRA certified handgun instructor and ran training and qualification courses for the local PDs and civilians.
Some of the stories he would relate to me up at hunting camp simply left me flabbergasted. He even had a spat with one of the police chiefs because he refused to qualify a few of his officers. Some were so bad that he told me they would hit 3' in front of the target (on the floor) at 12 yards!
I personally witnessed the ineptness of a local officer a few years ago. I hit a deer with my car coming home at night. The next morning I called the game commission and got permission to get it. When I arrived the buck was still alive and I called the Twp police to come dispatch it for me. After trying to shoot it in the head 4 times from about 10 feet I was about tempted to ask him for his sidearm so I could kill the poor thing. But he finally hit it in the head on the next shot about 5' away.
As for chambering, I have no problem carrying a 9mm simply for concealment (M&P Shield) but I feel much better when toting my 40 S&W or .45 ACP.