The cavity has been modified with what Mizuno calls a Stability Frame. This frame saves weight from heel of the club and moves it toward the toe to increase the MOI. This moves the CG (center of gravity) nearly 2mm closer to the center of the club, which makes it more consistent with less face rotation. The new frame also moved the CG down, resulting in higher trajectories and faster stopping power, allowing players more opportunities to be aggressive.
The head of the club looks more clean and traditional, but it is still made with the same material as the JPX 900 Hot Metal. The head is made from Chromoly 4140, which is a strong and flexible material that allows the face to be thinner resulting in longer shots. The face cup is created as a single piece and wraps around the chassis using a seamless construction for better feel. JPX 919 Hot Metal stops fast enough, as the landing angle was steeper to accommodate for the lower spin rate.
The Hot Metal set goes to a 45° pitching wedge followed by a new release of JPX 919 wedges in higher lofted wedges.
We recently conducted testing on the Mizuno JPX 919 Hot Metal. One of our Certified Custom Fitters compared the JPX 919 Hot Metal to the JPX 900 Hot Metal. They were both 6 irons with standard lie and loft. He used Dynamic Gold 120 shafts in both irons. Here are the results: