Yeah, I shot # 5 this morning, with greater effectiveness (it seems). My eyes are not all that great (for tracking, it seems ... too much computer time). And, yeah, I may even put # 4 on the menu.
While I was cleaning the bird I got yesterday I recovered some of the # 6 ... whoa they seemed small. I cut open a round of # 6 lead upland shells, to compare. Yeah, # 6 is too small for Mallards, except perhaps early in the season when they hardly have a layer.