I had a 28bore/.55" a few years ago. I think it weighed in at 7.5lbs.
Did just fine with ball (wadded) out to 50yds.
The biggest issue with them is VOLUME of shot. The bigger bores are more forgiving just because they just carry more shot. Still did pretty well for squirrel.
As for wanting a light gun, my Type G/Carolina Trade Gun has a 48"/20ga barrel and weighs 6lbs 2oz.
Makes my 8lb fusil de chasse feel like an artillery piece!
Mario