My worst was a High Standard Sentinel MK IV in .22 Mag. I bought it for a nice price, cleaned it up and went to the range.
With CCI Maxi-Mag 40-grain, it keyholed at 15 feet. With 3 other brands of ammo, it shot about about a 10-inch group, once again at 15 feet. DA trigger was horrendous, single action was still pretty stout.
Sold it with full disclosure to someone who wanted to load it up with snakeshot and use it for a trail gun.