I've just gone from 115 grain bullets, to 100 grain bullets, and it didn't change the POI. (Actualy tightened the group, but that could just be my handloading.)
It's most likely you're compensating for recoil that isn't there (Read: You're flinching), load some dummy rounds in with your live round and run them, if you flinch on the dummy round, you know what's wrong.
However, if it DOES turn out to be your gun, move the sight a bit to theee... Right? I wanna say right, but that could be the tiredness talking.