My daughter has a mossberg 20ga. youth model with a rifled slug barrel. It shoots better than any of my 12ga slug guns do. I have not played much with the range and bullet drop on it yet though. At 100 yards I can put 4 rounds in a 3 inch line with remington copper solids shooting off my lead sled. I am looking to get a 20ga next year to play with and to try some different slugs.
She shot her first deer last year with the muzzleloader I was carrying since the deer was at 150yards and I was afraid her 20ga bullet might drop too much. She made a nice shoulder shot and the deer went down 10 yards from where it was hit. The deer got up and moved before I could reload the muzzleloader again so I had her aim high with the 20ga and the bullet hit just slightly below her aiming point. Apparently it didn't drop as much as I thought it would, and the damage it did was significant.