Gregma
I'm assuming you don't see double vision normally. Look at a small object 10 - 15 ft away (a doorknob or similar size). Point your gun (after making sure it is empty and knowing there is a safe backstop) at the object. Close one eye and see where the gun is relative to the target. If it is on target, that is your dominant eye. If it is not then that is your non-dominant eye. Don't worry if you see two guns. If you see two objects, then you are shifting your focus. You can use your finger to do this exercise as well.
What some people tend to do is shift their focus which causes them to see two of everything because they are looking crosseyed. Or, they compensate by moving the gun or finger which negates the entire process. The idea is to point at the target in a way that feel most natural, then close one eye without moving your head or hand.
I'm assuming you don't see double vision normally. Look at a small object 10 - 15 ft away (a doorknob or similar size). Point your gun (after making sure it is empty and knowing there is a safe backstop) at the object. Close one eye and see where the gun is relative to the target. If it is on target, that is your dominant eye. If it is not then that is your non-dominant eye. Don't worry if you see two guns. If you see two objects, then you are shifting your focus. You can use your finger to do this exercise as well.
What some people tend to do is shift their focus which causes them to see two of everything because they are looking crosseyed. Or, they compensate by moving the gun or finger which negates the entire process. The idea is to point at the target in a way that feel most natural, then close one eye without moving your head or hand.