Several years ago I had the Mossberg 20ga bolt gun with a polychoke and sights on it. I managed to knock a grouse out of a tree with it and shot one or two crows on the wing. With practice, I also found it effective on clays. I fired a few slugs through it at the Hart House Range and found it effective at 20m (the length of the range), though he heavy trigger pull didn't seem to help much. I even took it with me one day for deer on a controlled hunt just north of Milton, though nothing came my way that day. It wasn't bad for the $120 that I paid for it.
I ended up selling it when I was in need of money and have since acquired a far nicer 20ga SxS that currently serves as my grouse gun. The only negative feature on it was that it sometimes had trouble feeding shells, and once managed to fire off a shotshell from an open-breach position. Interestingly enough, a few years later I read about Mossberg recalling a rifled slug gun that they built around the same action, claiming that exact same fault.
Cheers,
Frank