This is common for some people who flinch from recoil. You end up trying to compensate for the recoil by pushing the gun forward and down. Have your shooting partner sneak a snap cap in your mag, and when you try to fire the fake you may notice yourself flinch.

Or you gun just may be low.

You could also look at this chart...

http://www.homegunsafety.com/images/...tion_chart.gif