Mizuno Pro S-4: A Forged Iron Built to Launch Higher and Forgive More

Mizuno has a new forged iron aimed at a specific golfer: the player who loves the feel of a forged blade but wants a little more room for error. The Mizuno Pro S-4 keeps the clean Mizuno Pro look at address, then quietly engineers in more forgiveness. Mizuno calls it “Legacy Reborn,” and the idea is a muscle-back that launches higher and holds its line on a miss — without turning into a bulky game-improvement club.

The trick is where the mass sits. A redesigned curved muscle pulls weight lower in the head, paired with progressive offset, a wider sole, and a deeper center of gravity through the set. In plain terms: the ball comes off higher, the head stays more stable when you catch one off-center, and the long irons get easier to get airborne — the three things that make a players’ iron actually playable for more than a handful of golfers.

Feel is still the whole point of a Mizuno, and that comes from how it’s built. Each head is Grain Flow Forged HD from a single billet of 1025E mild carbon steel in Hiroshima, Japan — the process behind the soft, connected feedback Mizuno made its name on. A copper underlay softens impact further, Harmonic Impact Technology tunes the vibration so a flush strike feels solid instead of harsh, and a Triple Cut Sole bevels the leading and trailing edges to help the club slide through the turf. “The S-4 has been developed for players who appreciate the feel of a traditional forged iron but want greater confidence through increased forgiveness,” said senior R&D engineer John Freeman.

Out of the box it’s a committed build. Lofts run from a 21° 3-iron down to a 46° pitching wedge, lie angles step from 60° up to 63.5°, and the stock setup is a Dynamic Gold Mid 115 shaft in Stiff with a Golf Pride Z-Cord grip — a firm, mid-launch, players’ spec. It comes right-handed from 3–PW, and right- or left-handed from 4–PW. The full numbers are in the spec sheet below.

Here’s the thing about an iron this precise: those stock numbers are a starting point, not a fitting. A forged set lives or dies on lie angle — two degrees off and even a pure strike leaks offline — and a stiff Dynamic Gold shaft won’t match every swing speed or tempo. Before you commit to a build this specific, it’s worth reading your own launch numbers first. That’s exactly what our aboutGolf launch monitor at Under Par is for: dial in the loft, lie, shaft, and gapping to your real swing, so an iron this good performs the way it was built to — snow or shine, year-round in Muskegon.