Do you think your NID is a bit overchoked. Thats full in a 12. Extra full in 16 and extra, extra full in a 20. Might be approaching an obstruction in 28 or .410. Or is it?

Maybe we need to look st this differently. What is full choked in a 20? I know what the Briley choke chart says. But is that correct for guns built 50 years before wad design protected shot? I think .040, with hard shot and good wads is overkill. Might try a couple fiber wad loads to see if .040 makes sense in a 20.