And trap shooters are goofs of the first water as has been documented jillions of time. Mr. Yardley says that a shotgun stock should be just barely long enough that the thumb doesn't get jammed up the nose. My own experiments w/ a mucho adjusto stock give him high marks. His other criteria is that the trigger hand elbow should make a 90degree or less angle when the gun is mounted. Casual observation on my own again gives it to Mr. Y's instruction.
Course that's all just for shotguns. Rifles you on your own.
HTH
Dr.WtS