Shooting free hand or from a rest?
It might be you.
Are you anticipating recoil any?
Mix in some dummy rounds with your live rounds and try it then. You may find you are anticipating recoil a little and dipping the gun slightly before it goes off.
If you don't have any snap caps, try the dime drill. Put a dime flat on your front sight like forming at "T". Dryfire and make sure you are keeping the dime from falling off the front sight. If you can shoot it like that with live ammo and it is still printing below point of aim, then you can try some mechanical/ammo changes.
Personally, anytime a gun doesn't shoot to where I think it should, I assume it is the shooter. (ME) I have been right about that almost every time.