Different ammo, as Mark says, could be the answer. Also, is that from a rest or free hand? I believe there is a 'Shooting Aid' posted on a thread here, somewhere. You might try to find that & see if it gives you a clue.
Lastly, I haven't done much reading on the Remington, but is it possible it uses what some refer to as a 'combat' sight picture with the front sight on the center of the bull? I don't suppose that would cause it to be a whole foot low, but may be part of it.