... You've no doubt checked this already, but is the front sight 'way off to one side or the other? If so, use an allen wrench (3/16" IIRC) to loosen the sight, center the sight itself on its base, and cinch to screw down tight.
How do I know about this? Simple: had an M1with the same problem.
BTW: rear sight moves in the direction you want the impact to move; front sight is opposite. thus:
Rear. Impact
Moves Moves
Left. Left
Front Impact
Moves Moves
Left. Right
HTH -- without confusing the issue.
Ben Hartley