Mizuno Releasing JPX 921 Irons: Full Preview

Fans of precision forging and world-class iron design rejoice because launch day is finally here.  After some early teasing on social media, Mizuno has officially given us the full rundown on its all-new JPX 921 lines of irons, and there is a LOT to be really excited about.  

Looking to build off the success of its JPX 919 lines (and JPX 900 too for that matter), and when you already have some of the best irons on the market, there are two ways to approach a new release: revolutionary change or evolutionary change.  As you will see, Mizuno has given us a lot of both with its latest iron sets: the JPX 921 Tour, Forged, Hot Metal, and Hot Metal Pro.  We dive into each of the four lines below, and although it isn’t its own line, Mizuno also has a little something special to offer lefties too. We have a ton of information to cover, so let’s dive in.  

JPX 921 Forged

The largest technological leap comes in the JPX 921 Forged irons, but like a lot of the best stories, I think it makes sense to start at the end and work back to see how we got there.  Here we go.  The JPX 921 Forged irons have a higher coefficient of restitution (COR) that is approaching the legal limit (which translates to a better transfer of your club head speed into ball speed), and that higher COR is delivered over a larger area – an area that is about 45% larger.  And no, that is not a typo and I did not miss a decimal point. All of that power packed into a player’s profile head that is actually smaller than the JPX 919 heads.  

Holy Chromoly – I hope I have your attention and you understand that the JPX 921 Forged definitely fall into the revolutionary change category.  So how did Mizuno make what may just be the perfect blend of power and precision?  Well, the JPX 921 Forged irons are Mizuno’s first full body chromoly forged irons. 

Forged is a bit of a buzz word in golf and it can be used to describe a whole lot of things in irons, but Mizuno isn’t messing around with the JPX 921 Forged.  Unlike several “forged” irons on the market, such as those with only a forged face or a forged body with a welded face, the JPX 921 Forged irons use the same grain flow forging process that Mizuno is famous for to create this full body forged head.  Just like the JPX Tour and several MP20 sets, the JPX 921 full body chromoly forged irons are forged from a single billet and undergo a multi-step, labor intensive process to transform a cold, solid billet of 4120 chromoly (an incredibly strong steel alloy containing chromium and molybdenum) into a red-hot solid billet that is stretched, bent, and pressed and ultimately reaches its final solid iron form.  And unlike a casting process that will inherently create some inconsistencies within the metal, Mizuno’s forging process makes hyper consistent, quality irons without disrupting the metal grain structure.  Once the forged JPX 921 head is created, it is then back milled to create a “rebound area” that allows the face to flex and fully utilize the Chromoly alloy’s strength.

Even with the all new full body forged chromoly head and a hotter face, Mizuno wasn’t done.  Mizuno redesigned the head profile to be an even sleeker, more compact player’s profile.  This was accomplished by altering the blade length to be marginally shorter throughout the set and by reducing the offset in the 4-8 irons, as compared to the JPX 919 Forged. In other words, the JPX 921 irons are truly a player’s forged iron that feature a small body, minimal offset, and thin top line.  But remember that revolutionary aspect – despite the smaller profile and shape, the sweet spot size is essentially unchanged from the JPX 919 irons.  

The Power Frame and back of the JPX 921 Forged irons have also been redesigned and re-engineered to improve forgiveness and sound.  For example, the redesigned Power Frame redistributed some toe weight into other portions of the Power Frame, resulting in more perimeter weighting and a wider milled back slot. This subtle change should improve forgiveness on off-center strikes and also promote a slightly higher launch.  With this additional launch, and in order to maintain proper launch windows, the lofts of the 4-8 irons have been strengthened by one degree.  The JPX 921 Forged set is comprised of the full body forged chromoly 4-7 irons and full body forged 1025E 8-GW irons (the same material in the JPX 921 Tour), which further illustrates the perfect blend of power and precision.

The JPX 921 Forged will come stock with Nippon Modus 120 Stiff / 105 Regular shafts and Golf Pride MCC +4 Grey grips.  Unfortunately, they are only available in the 4 and 5 irons for left handed players. 

JPX 921 Tour

While the JPX 921 Forged are unquestionably a revolutionary change, the new JPX 921 Tour irons are more of a natural evolution from the immensely popular JPX 919 Tour irons.  Like its predecessors, the JPX 921 Tour irons are precision instruments in the right hands.  

Mizuno’s Tour irons need no introduction for passionate golf fans.  An absolute mainstay and money making machine on Tour, the JPX 921 predecessors (the JPX 900 and JPX 919 Tours) have been in the bag for several major championship wins, and collectively, have the honor of being the most used by non-contract players in 2019 and having the most money won by non-contract players in 2019.  Needless to say, Mizuno already had a major winner (yup, word play, sorry) on its hands and the new JPX 921 Tour irons contain subtle but noticeable improvements to the Tour’s impressive heritage and lineage.  

“The Chosen One.”  Mizuno clearly believes its refinements has made the ultimate Tour iron and the JPX 921 Tour has a nickname to match that confidence, with Mizuno calling it: “The Chosen One.” By all indications, the JPX 921 Tour has every chance to live up to this lofty moniker. Let’s finally dive into how Mizuno maintained the revered shape and profile but still improved its Tour irons.

First, weight re-distribution.  Mizuno wanted to redistribute some weight away from the toe and into the rest of the back of the club, which provides slightly more perimeter weighting.  According to Mizuno, this weight redistribution will subtly improve the feel of the club while still remaining toe weighted.  In other words, the JPX 921 is still toe weighted but just a little less so.  As discussed above, the redistribution of some weight into the perimeter should also subtly improve launch conditions. But subtle is the key word here – Mizuno only needed to make minor alterations with this weight distribution to improve feel and launch but without losing the toe weighting design that is so well liked by the best players.  

Next, Mizuno altered the sole widths.  The new JPX 921 Tours feature thinner soles in the short irons (9-P) and slightly thicker soles in the long irons (4-6).  This will improve turf interactions with the scoring irons while slightly lowering the sweet spot and improving launch in the longer irons.  Internal Mizuno testing actually shows that the combination of the weight redistribution and the sole changes resulted in the sweet spot height being lower throughout the entire set (4-P), although it will be most “noticeable” in the 4-7 irons.  

Another change in the JPX 921 Tours is a shortened CG (center of gravity) distance from the shaft axis, also referred to as shortening the length of the CG.  Translated, this means that the CG has been moved closer to the hosel as compared to the JPX 919 Tour irons, but it will be further away from the hosel as compared to the JPX 900 Tour irons.  As a result, the JPX 921 Tours can work the ball easier.  Although Mizuno doesn’t expressly say it, this is a logical byproduct of the reduction in toe weighting and the distance of the CG for the JPX 921 set will be squarely in the middle of the JPX900 (shorter CG distance) and the JPX 919 (longer CG distance).  If Mizuno is right, it has struck the perfect balance between the competing needs of workability, ideal toe weighting, and keeping the CG from being too close to the hosel. I expect this change will be well received by the better players among us. 

Finally, we know that feel and sound are correlated so Mizuno paid extra attention to sound through extensive acoustic testing.  Mizuno says that the new sound has less higher frequency sound pressure and more of a traditional iron sound at impact.  Truly no detail was too small.

Continuing the forging tradition that Mizuno is famous for, the JPX 921 Tour irons are made from 1025E Pure Select Mild Carbon Steel using the same Grain Flow Forging at the same facility in Hiroshima Japan.  As a result, the JPX 921 Tour irons will have the same identifiable and unsurpassed feel that Mizuno has built a reputation of delivering.  It isn’t often that a marketing slogan turns out to be true year after year after year, but the attention to detail and process is the reason that truly “nothing feels like a Mizuno”.  Clearly, the JPX 921 irons are the result of meticulous design and attention to detail with extensive Tour testing and prototyping to get it just right. 

The JPX 921 Tour irons are available in a 4-GW set for right handed players and 6-GW for left handed players. Both will come stock with KBS S-Taper shafts and Z-Grip Full Cord grips. 

SEL – Special Edition Leftie

Although the JPX 921 Tour and Forged offerings are somewhat limited for left handed players, Mizuno is offering a special combo set that is called the SEL, or Special Edition Leftie.  The SEL set is comprised of 4-5 JPX 921 Forged and 6-GW JPX 921 Tour, giving the lefties among us a perfect blend of forged chromoly goodness in the long irons with the 1025E forged Tour irons to score.  The SEL set comes stock with KBS S-Taper shafts and Z-Grip Full Cord grips.  

Hot Metal / Hot Metal Pro

Rounding out the new JPX 921 line are Mizuno’s original chromoly irons, the Hot Metal and Hot Metal Pro.  These multi-thickness chromoly 4140M faced irons are back and better than ever.  And by better, I mean faster. Mizuno has pushed its chromoly manufacturing capabilities closer to its limits by reducing the center thickness of the seamless face cup design to a mere 2.2 mm thick.  But this reduction did not require adding any thickness to the remainder of the club face, which remains at 1.9 mm thick.  Building off this base, the Hot Metal and Hot Metal Pro irons are poised to deliver faster ball speeds because when it comes to speed, thinner is better and Mizuno is taking thin to the extreme.  

Of course, the face is only one part of the equation when it comes to ball speed.  To promote maximum flexing, the JPX 921 Hot Metal and Hot Metal Pro irons have been redesigned with a variable thickness sole that allows the sole to flex and stress.  When the sole can flex and absorb some of the stress of impact, the face is free to flex even more. By incorporating a selectively thinner leading edge paired with thicker areas toward the heel and toe, the Hot Metal and Hot Metal Pro irons are able to achieve a higher COR.  And like the Forged irons, Mizuno was able to also increase the COR Area.  The combination of the thinner face, the seamless cup face, and variable thickness sole directly translates into faster ball speeds over a larger portion of the face.  

That isn’t empty talk – Mizuno backed it with robot testing data. Ball speed retention on off-center shots was shockingly high, with the lowest point being 95.4% retention and the highest being 98.7%.  Now, that’s innovation I can get behind.  

As with the 919 models, the JPX 921 Hot Metal and Hot Metal Pro have a low and deep CG for forgiveness and high launch, but this year the lofts have been strengthened slightly by one degree to bring its irons more in line with the competition.

The JPX 921 Hot Metal and Hot Metal Pro irons also had their Stability Frame redesigned to save discretionary weight, move weight toward the toe, and to deliever extreme perimeter weighting for forgivingness and MOI on off-center strikes.  In changing the Stability Frame, the acoustics were also refined by adding three more “Sound Ribs” (for a total of 8) to the cavity of the club to produce a slightly more solid sound at impact.  

Both the Hot Metal and Hot Metal Pro sets come with what Mizuno is calling their Specialist Wedge Profile for at least the GW, and in some rarer instances the SW and LW too.  This specially designed wedge is intended to make a smooth transition from the set irons toward traditional wedges while maintaining head size and specifications that will flow naturally from the irons, and feature quad cut grooves, CNC milling, and wedge grind.  

The main differences between the Hot Metal and Hot Metal Pro irons are the head length and offset.  As was the case with the 919’s, the Hot Metal Pro heads are noticeably smaller and have less offset.  While that remains constant, the overall head size of each set has marginally increased and, as a result, the offset in both sets was also increased.  Despite these increases, neither set should ever be confused as being draw biased. 

Regardless of if you prefer the full size and power of the Hot Metal or prefer the smaller head and less offset of the Hot Metal Pro, Mizuno has a set of JPX 921 Hot Metal irons that are certain to power your game.  The Hot Metal irons come stock with either Nippon NS Pro 950 Neo or UST Mamiya Recoil ESX shafts and Golf Pride MCC +4 grips.  The Hot Metal Pro irons come stock with the Project X LZ Black 5.5 shaft and Lamkin ST Hybrid grips

The JPX 921 lines of irons will be available for pre-sale on August 31st and available in stores on September 17th. There is so much to discuss with the JPX 921 irons and I hope that you will ask any questions you have below or in the forum.  Believe it or not, there is even more information that couldn’t be squeezed into this article, so be sure to check out the THP forum for even more information.  I also hope you appreciate that I waited until this point to point out the absolute most obvious thing, the JPX 921 irons are absolutely beautiful and will turn heads in your bag.  

You can learn more by visiting Mizuno at www.mizunogolf.com.

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Gary C.
Gary, an upstate New York native currently residing in Virginia, is a low-teen handicap with aspirations of single digits someday. Although he picked up golf later in life, Gary enjoys learning everything possible about golf equipment and skills to make up for lost time. As a result, Gary loves to tinker with his clubs and swaps things in-and-out of play with regularity. In addition to being a veteran of several events, Gary is happy to discuss equipment, technology, and accessories with anyone that is willing to engage.
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