I shot an XD-40 at the range a few days ago and started off right on target (within the 9 point target ring). After about 50 rounds I started to move to the 8 and 7 point rings and shots moved all over. Without actually seeing me shoot, is it more than likely lack of stamina due to not having been the range for about 2 months, sight picture, or something else? Not sure if this is common among shooters, so I wanted to through it out to the group.