Mizuno JPX921 Hot Metal and Hot Metal Pro Iron Review

Published: 10 August 2020 Last updated: 06 October 2023

At a glance
TG Rating 5 out of 5
Owner Rating Not yet rated
RRP £135.00

What we say...

The new Mizuno JPX921 Hot Metal and Hot Metal Pro golf irons combine forgiving cavity-back performance with fast ball speeds and high launching shots.

When Nike pulled the plug on its golf club business in August 2016, it sent shockwaves through the game and meant big-name players like Tiger Woods, Rory McIlroy, Brooks Koepka, Tony Finau and Paul Casey were all left without equipment contracts, which was unprecedented. But nobody could have predicted how Nike’s exit would help Mizuno, and ultimately lead to this new JPX921 family of irons.

Four years ago, Mizuno were still seen as a traditional forged iron company, the type that made brilliant musclebacks with shiny finishes (that are bought by less than 1% of golfers). With sales of forged irons falling, the JPX family – with their funky colours, cartoon-style ads and satin finishes – we’re designed to draw in a younger audience, but they failed to generate the sales Mizuno expected.

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Mizuno JPX921 Hot Metal Iron

Step forward Mr Koepka (the person Mizuno had created JPX for, before Nike swooped in and signed him). As a free agent he decided the JPX900 Tour irons were the perfect fit for his game. He liked them so much, he was happy to play them for nothing. Koepka then went on to win the 2017 US Open, defend that title in 2018 and bag the US PGA, all with a set of Mizuno irons. The feat single-handedly rebooted Mizuno’s JPX iron family and attracted that new, younger golfer.

Once Mizuno revealed its replacement, the JPX919 Tour, Koepka put them straight in play and won his fourth major (another PGA) in 2019. So Koepka single-handedly has been the making of JPX, and with the family now being two years old Mizuno have revealed their successors.

Mizuno JPX921 Hot Metal Pro iron

Mizuno JPX921 Hot Metal Pro Iron

RRP: £135 per iron

Availability: 4-GW

Stock shaft: Project X LZ Black 5.5

7 iron loft: 29°

Mizuno say the success of the Hot Metal Pro iron rests on how many ‘players’ they can convert to this new cast model. For the best part of the last 12 months the previous JPX919 Hot Metal Pro has out sold the JPX919 Forged (that’s a first year product against one in its second), now the two go head-to-head in a brand new product range.

Any decision between them is likely to come down to how much premium golfers put on a Mizuno Forged feel (the JPX921 Forged) over the cast chromoly Hot Metal Pro. We’re talking fractions but the longer irons are a little larger, the short irons are slightly more compact, and offset across the set has reduced a fraction to match the JPX 921 Forged.

Mizuno JPX921 Hot Metal Iron

RRP: £120 per iron

Availability: 4-GW

Stock shaft: Nippon NS Pro 950 Neo (s) UST Recoil ESX (g)

7-iron loft: 29°

Chromoly 4140M steel is now in its third generation of iron, and at Mizuno that means the tech has matured. Mizuno have made the Hot Metal from the same material for two previous product cycles (four years) which means they know how best to use it, and it’s likely they’re close to maxing it out.

The game improving Hot Metal is cast, and this one has grown fractionally in blade length for the long and mid irons where the short irons are more compact. There’s also a little more offset across the set.

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What you need to know about the Mizuno JPX921 Hot Metal and Hot Metal Pro irons

Maxed out

Mizuno say thanks to having four irons in the JPX family everything about the Hot Metal and Hot Metal Pro irons canbe a little more maxed out for their target golfer. It means the Hot Metal Pro is a little more compact, with less hosel offset. While the Hot Metal has a slightly longer blade length and a bit wider top edge to enhance forgiveness.

A little less loft

Mizuno have never played the loft jacking game, as they insist a 7-iron needs to take off and land like one. The JPX921 Hot Metal and Hot Metal Pro are though one degree stronger in loft than previous models.

Hinge and flex

Both new JPX921 Hot Metal irons have a variable sole thickness so the leading edge can behave more like a hinge, and allow the face to take on more flex. Mizuno say not to expect huge gains in ball speed and distance (maybe a couple of yards) from the previous JPX919 Hot Metal models, but there should be a decent step up from the four year old JPX900 Hot Metal.

More solid

Three new sound ribs inside the irons cavity back not only strengthen the structure to reduce vibration, they also free up extra ineffective weight. It means golfers get a better feeling iron that’s also slightly more forgiving on mishits.

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Mizuno JPX921 Hot Metal Iron