It could be the shafts, It would be real easy to pull the shaft from one of the Nike irons, and replace it with the same shaft as you have in the other set. Then you'd know for a fact if it was the shaft or not. One question I do have for you. Do you hit the Nike irons as well as your other set? If you are making better, more solid contact with the old set, that could explain the extra yardage over the Nike irons. If contact is solid with both sets, then by all means, replace one shaft in the Nike's and see if that's the cure. How about ball flight? Is one much higher than the other? Sorry, I think I just asked a second question.