There are various definitions of "turkey shoot",one of them is derived from the historically early one that Wade provides, and one of them actually contradicts the early one. The derived definition is "a shooting contest in which the targets are moving turkeys". Because the earlier definition involves a difficult task that Wade well describes, it is surprising that a more recent definition of a turkey shoot is an "easy task". A more recent and more specific definition is an easy military task, especially "easily shooting down enemy aircraft when the enemy pilots or planes are inferior". This usage appeared after the battle of Midway in the Pacific during WWII. If I recall my history correctly US ships and planes shot down about 400 Japanese planes during that battle, with far fewer US planes lost. This "easy" victory in the air was called a "turkey shoot".

Bob