I found this on the net it describes my problem:
“Milking,” taken from the hand’s movement when milking a cow’s udder, occurs when the index finger closes on the trigger and the other fingers sympathetically close with it, changing the grasp and pulling the sights off target. Most commonly, this will pull the shot low and to the side of what you were aiming at. It is a function called “interlimb response.” When one finger closes, the other fingers want to close with it.
Also, what are snapcaps?????