James I think I have learned (from you and lots of field/hunting experience)Light guns are 6lbs- ish and under.
Over 6lbs ish they are "guns".....over 7.5lbs they are "duck guns". Once they are over 8lbs they are good Duck guns.....
Lots of guys shooting upland birds with 7lb guns. Lot of Fox and Parker 12's are high 6lb-7lb range. Nothing wrong with that but they aren't light.
For hunting clear cuts and messing around with a light gun try and find an old beater Fox Sterlingworth 16 or 20 bore preferably with 26" barrels. They will be at or just under 6lbs often. Nice little guns but you probably wont find one. they are rare (and I will try and buy it before you.