It could be several things ... which is why any answer is a guess. Even though your LW has only 7 of bounce, the leading edge could be high; it could have a wider sole; It could be you. A lot of skulls are caused by tension ... a quick transition, too armsy ... an unrelaxed swing. You've got to work it out. And now I realize this is a 6 yr old thread that someone rejuvenated.
8/2/15 at 2:12pm