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| October 19, 2019

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Review: ProWin M4/AR15 Hop Unit -

Review: ProWin M4/AR15 Hop Unit
Dave Miller

Review Overview

Delivered Accuracy
Quality of Air Seal
Ease of Installation


An excellent unit, delivering exceptional accuracy and air seal. Let down only by the lack of spring to push it against the gearbox.

There are many hop units for M4 users to choose from. They range from outlandishly expensive (prometheus strike chamber) to questionably cheap (some of the cheaper ACM brands).

Most of them use the standard three gears design. At the time of writing two readily available hop units use a much more precise system – the Madbull Ultimate and this, the ProWin M4 Hop Unit.

Strikingly different to any other hop unit design, the ProWin Hop unit is bright blue and chunky. It is provided with a set of very well moulded plastic parts. The hop is adjusted via the large ring on the back, which has a spiral grove in it that moves the hop arm.

This ring sits on top of an o-ring that stiffens the adjustment up, meaning it won’t move by itself. The hop arm sits tightly in the spiral groove, and also sits tightly between the two sides of the hop chamber – eliminating play. In fact there isn’t any play in this hop unit at all, it is absolutely rock solid.

The one minor let down with this hop unit is the lack of spring. A grub screw is supplied that is designed to push the hop unit back against the gearbox, but that really isn’t a good alternative to a spring. I solved this by using half a long shaft motor spring to push the hop unit back, it works perfectly.






On fitting the hop unit to my m4 the muzzle velocity jumped from 330-360fps. Running this unit with a H-nub and an A+ hop rubber delivered what felt like pinpoint accuracy. I say felt like as I never did any groupings, but I found that I could consistently hit the other team at ranges and with an accuracy that I previously did not have. I’m not the only one to have such experiences either! Mike, another one of the writers at AO bought one and dremelled it a bit to fit in his WE Katana.

The result was a trip to the shop to get it chrono’d at 390fps – a 50fps boost – before having the spring changed.

Hop units really are the foundation of an accurate gun, and this one is – in my opinion – the best one money can buy. It has very very precise adjustment, excellent seal quality and zero shift. It is incredibly well machined (entirely from a small chunk of aluminium, no casting here) and finished to a flawless quality. It also happens to be affordable, at around $21 dollars depending on where you get it from. I like it so much in fact, that I have just bought a second one for my short AR upper! This new one (as you can see in the photos) comes in a much more matte finish than my old one, which is about 18 months old now. The quality however, is still there.

If you want to increase the accuracy of your AR15, then look no further. Yes a tightbore barrel will probably help, but the increase compared to cost for this hop unit far outweighs all but the best of inner barrel upgrades.