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ProWin M4 CNC Hop Up Unit

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Free Shipping on Orders $200 or More ($9.99 for orders under $200)

Fox Airsoft offers a 30 day warranty and return policy.

About the Prowin M4 CNC Hopup Unit

This M4 hopup unit by Prowin is one of the best made units out there. Constructed of durable CNC aluminum, Prowin hopups are held to the best tolerances which produce the most consistent performance in accuracy and velocity for an M4 style AEG.

Hop up chambers go through a lot of use that people do not often know about or consider. During the loading process, it is the bottom of the hop up unit where the magazine meets it that goes through wear and tear. Plastic units could get damaged if the magazine is inserted improperly and with too much force. Plastic units might also become brittle if it is very old and can chip or crack just from age.

These aluminum units are not only stronger but precision made as well. Some guns may already have metal hopup units and those will work fine. So why would this be an upgrade? Cast units are made from molds and use lower grade material that although seem fine, could contain imperfections that could affect performance or all in all could be better if you are trying to get the most out of your gun. These CNC units are precision machined rather than cast, so every detail and every part of the hop up unit will be made to precise dimensions making it tolerances very consistent which translates to consistent performance and fitment too.

Another thing and probably the biggest thing consideration is performance. Having a fine crafted hop up unit that engages properly and is free of defects can only improve performance. One problem guns with poor air seal and out of spec hop up units we have observed a bump in fps simply by changing the hop up unit.

These hop up chambers will work for most M4 style guns out there. We have not found them to be compatible with ICS and Classic Army unless the barrel is reconfigured as well (not recommended).

If you need help or consultation on repairs you could give us a ring at (888)316-7816 or shoot us an e-mail at The senior staff and owners of the company have been playing for well over 15 years and certified and authorized by several major manufacturers to do OEM quality repair and warranty work.

Note: Fox does not warranty or accept returns for parts that have been installed/attempted to be installed.

Note: Due to varying manufacturer tolerances for gearbox internals, parts compatibility no matter what version might NOT fit even if it is supposedly correct and fitment is NOT guaranteed. The reality is that some parts may need fitting and some parts might look the same but the dimensions are slightly different enough to not work. This will require technical experience to identify to overcome.


Quick Look:

  • CNC aluminum construction
  • Precise dial adjustment
  • Requires Hopup bucking and nub for install

What's Included:

  • CNC Aluminum hopup unit, hopup wheel, spacer arm

Alternate Lookup:

  • PW HU M4

— Customers Testimonial —

Honestly, this is the only airsoft shop I will ever buy from. Their guns are always quality. Their custom work is mind blowing. Their staff is not only helpful, but always happy to help. If you are just starting out or have been playing for years, these guys have guns, gear, and good advice for every situation.
— R. King
Awesome company and products. Received sooner than projected from Colorado and I'm in California. Less than 2 days from placing order to receiving it. . Everything shipped as ordered . Incredible selection and great price... Did my homework and eventually came back to them. I'm glad I did. My squad will be ordering and I be ordering more gear as well.
— John
Great people great place I've ordered a few small things. Delivery was on time both times great items. Yesterday I checked my mail they sent me a fox airsoft patch just to say thanks and to me that's a way to do bussiness. Fox y'all have got business keep up the good work.
— Matt
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