Mizuno JPX S40 – Largest Forged Mizuno

I’ve read through the Mizuno Japan website and the translation of the transcript from the above video.  It appears the Mizuno JPX S40 is set to be released in March 2026.  I don’t recall seeing additions to the JPX line in between cycles before, but this is an interesting club.  They describe it as the largest head among Mizuno’s forged irons.  It appears to be a super game improvement style iron, but forged.  This should give an excellent combination of forgiveness combined with the best Mizuno feel.

They also say they have strengthened the face of the iron by 30% compared to conventional forged irons which has created a high rebound.  With the improved technology in irons, faster faces actually means not just long distance when hit well, but also means they can speed up the area surrounding the sweet spot for more even ball speed across the face.

Mizuno says the JPX S40 has boron but describes it as soft iron boron, which is maybe some form of alloy.  They claim boron core combines excellent forged feel with high rebound performance. The translation describes it as mild steel boron steel (S25CB) – “A soft material for hitting feel and a strong material for resilience” Mizuno claims it is softer than the chromoly (SCM435) used in many of their current forged long irons and it is stronger than the forged steel used in their short irons (S25CM).  It is softer than chrome molybdenum steel (SCM435) and stronger than mild forged iron (S25CM – also known as 1025E).

The 5 iron, 6 iron, and 7 iron have a micro-slot that penetrates from the sold to the cavity side, along with 18g of tungsten weight mounted in the micro-slot region.  Tungsten will lower the center of gravity, giving the ball a higher launch.

They use the Mizuno HD Grain Flow Forging, giving the irons the unique Mizuno feel.  There is a resin badge in the cavity which mutes vibrating during impacting, further improving the feel.

So the Mizuno JPX S40 is a large, cavity back forged iron, with boron, tungsten, and a micro-slot.  This combination should lead to excellent feel, high ball speeds, and ease of launch.

It does seem like this will be a Japan only release for now.  I know Japanese clubs do make there way to the states though sellers, but it’ll be interesting to see how these compare to the Mizuno 925 JPX Forged, which is their forged player’s distance iron right now.  The S40 seems like a larger size, but the 925 Forged is already very forgiving.