RE: How much should a lead a Mallard with a 12 ga?
I would sugges some time on a skeet field shooting low gun. Shoot your target pass thru or pull away style ,either one or combo of both. Focus on your target and forget about your gun. DO NOT shoot sustained lead, that lead to measuring your lead and eventually stopping or slowing you gun.
Your brain is the best computer for figuring out lead and if you focus on the target be it clays or live birds ,with a little practice and good shooting form ,it will do what comes naturally and you'll be dropping those mallards in no time.