Sub 70 639 MB Irons

The 639 MB iron is Sub 70‘s muscle back offering for players that want a relatively compact head and premium control. Each head is fully forged with the back being milled to give the club a unique look and precise balance. While definitely a true player’s club, the more moderate face size and slightly stronger lofts may make the 639 MB play a little easier than a traditional MB blade.

The Looks

At address the Sub 70 639 MB certainly looks like a blade, but the size is just a touch bigger. I can’t emphasize “just a touch” enough. By no means is it a large head, but it doesn’t look like a baby blade behind the ball. Overall, I would still consider this to be a compact club head. The topline is relatively thin and the offset progresses through the set nicely.

Sub 70 utilized a custom milling process to finish the back of the club head. You can see the lines milled into the top half with circular milling on the muscle of the club. I sort of feel like the overall aesthetic is “modern mechanical” but with a touch of class and elegance.

If you prefer a more traditional finish, Sub 70 also offers the 639 MB in a brushed/satin chrome finish. The PVD black pictured here will wear a little faster, but that’s fairly common for black irons. That just means if you’re a good ball striker, you’ll get those dime-sized wear spots in the face quicker to impress your playing partners.

How Does it Feel?

Much like my review of the 639 CB, the Sub 70 639 MB feels excellent and impresses at half the price of its major OEM competition. Paired with the right shaft, the 639 MB feels extremely crisp and responsive with a somewhat generous sweet spot. Like I mentioned earlier, the club head is a touch larger so that contributes to the expanded sweet spot. Additionally, you will see in the pictures that most of the muscle’s mass is focused toward the center of the club face. This concentrates the center of gravity (CG) and also helps make the club feel a little sweeter. The overall feeling at impact is very pure and exactly what you look for in a muscle back iron.

Though the 639 MB sole is on the thinner side, the slightly rounded leading edge and sole shape help produce a smooth, yet crisp, feeling through the turf. Don’t get me wrong, like any blade MB, the 639 MB can dig, but that’s on you to control. Assuming you have the game to play a MB, you’ll find the turf interaction quite satisfying with the 639 MB.

How Does it Sound?

Sound is pretty straightforward for the Sub 70 639 MB irons. A nice swing with clean contact gives you a nice “pick” sound. Swing a little faster and that “pick” might take on a little more of a “whack” characteristic. The sound from the turf interaction is a pretty standard “rip” sound. Take the club down a little steep and you’ll get a thump from the turf. Go too deep and the sound is your standard fat shot, not that I would know. But again, that’s on the player, not the club.

On-Course Performance

In the current climate of long distance irons and floating faces, muscle back blades are still relatively unchanged. Their whole purpose is to allow a player to have total control of the golf ball and super precise feel. That’s exactly what the Sub 70 639 does. True, I spoke about the sweet spot being slightly larger which makes a pretty big difference by seemingly adding a little forgiveness. Let me be clear, that’s forgiveness in terms of a standard MB blade, not in the sense that it will bail you out of terrible shots. In my testing, the 639 MB performed incredibly. It was easy to work the ball and play target golf.

One other note to point out is the lofts are slightly stronger in the 639 MB. This was done for a couple of reasons. The muscle on this club is slightly beefier than MBs from the old days. As such, the CG is lower in the head and produces a more mid/high flight as opposed to a low bullet. The lower lofts help make up for that higher flight to get more typical distances of the club number.

The second reason for the stronger lofts is to better accommodate creating combo sets with the Sub 70 639 CB. With lofts that lineup with the CB irons, it allows golfers to make the transition at any point in the set without significant differences in flights.

Final Thoughts – Sub 70 639 MB Irons

My common take on Sub 70 Golf is that the gear more than holds its own against mainstream competitors. Comparing the 639 MB to other muscle backs from major OEMs, they certainly belong in the conversation. When you factor in the price tags, the argument only becomes more compelling. At the end of the day, the Sub 70 639 MB is a player’s blade that delivers premium performance and feel at an affordable price tag.

Stock Sub 70 639 MB Irons Specs

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