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ProWin M4 CNC Hop Up Chamber For Marui M4 (AEG)



ProWin - M4 CNC Hop Up Chamber For Marui M4 (AEG), delivers more range and improved accuracy from your Arisoft AEG. Designed for primerally M4 AEGs but may be compatible with other AEGs that use an M4 style hop unit. Not only does the hop unit look good it performs amazingly. With a highly precise and precision tuneable rotary hop wheel you can add micro hop adjustments to any weight BB. An ideal upgrade for any Airsofter and combined with the right FPS you can easily lift up to a 0.36g BB or heavier. Once fully built this hop unit is solid, with zero side hop arm movement your shots are far more consistent in fight path on every shot. We recommend you combine this hop unit with high quality BBs for truly outstanding results! Please note there is no hop rubber or nub included!

  • Easy Build & Installation
  • CNC Machined Aluminium
  • Improved Accuracy & Range

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Product Details:

  • Name Designation: M4 CNC Hop Up Chamber For Marui M4 (AEG)
  • Manufacturer: ProWin
  • Construction: CNC Machined Aluminium Body
  • Compatibility: Most Airsoft M4 AEGs


  • Incredibly precise and fine hop adjustment
  • No side hop arm wobble
  • Adjustable grub screw hop spacer
  • Easy installation!
  • Improved range and accuracy
  • Everyone who works at Patrol Base loves this hop unit!

Package Incudes:

  • 1x CNC Hop Unit
  • 1x Retention / Seal O-ring
  • 1x Polymer hop arm
  • 1x Polymer barrel C-clip
  • 1x Hop arm pin
  • 1x Adjustable hop spacer grub screw
  • 1x Precision adjustable hop wheel & wishbone retention

Buying with confidence is important and knowing that we have a no quibble returns policy will hopefully put your mind at rest.

Items must be returned in original packaging! Any faults or damage must be reported as soon as the item has been opened. If we believe damage has been inflicted by yourself, we reserve the right to refuse a return and/or refund of the item and postage.

Any returned item/s returned due to a fault or incorrectly dispatched will have your postage REFUNDED. If you are returning an item due to incorrect sizing or being unwanted you will not be refunded for return postage. To receive a full refund of your item/s you must contact us within14 days of original delivery date in original packaging. 

The stated Feet Per Second listed (FPS) is based on the first unit taken into stock from our suppliers. We check this ourselves in store using SKANAR Chronometers. Subsequent units on new deliveries or new production runs may deviate from this figure substantially. If the power level of the unit is of particular importance to you, the end user, please contact us at the time of purchase and we will try our best to cater to your needs.

11.1V LiPo batteries are for use in highly tuned and modified AEGs ONLY. The use of an 11.1V LiPo, 10.8V NiMh/NiCd or higher voltages voids all warranty on all AEGs supplied by Patrol Base Ltd. This includes units where Manufacturers, suppliers, other retailers or the Airsoft media state that a unit is 11.1V LiPo ready.

Modified Returns

Please note, we can only accept returns which are returned to us unmodified from their original state. This includes changes or permanent modifications to the Internal or External components of the weapon, included but not limited to: Gearbox Work (Such as Gears, Pistons, Triggers, Nozzles and Motor), or Barrel Cutting, Changing, Spraying of the Weapon, Removal of Two-Tone. This includes disassembly weapons, with the exception of expected maintenance (Such as Pistol Cleaning, or Barrel Cleaning).

We cannot accept returns which have had work carried out by other Retailers, or Airsoft Techs such as an attempted repair. 

User Error

If any problems arise from user error we cannot accept a retun, however we will help you in repairing the problem. Examples of User Error are, and not limited to:

  • Weapon Modification
    We do understand that users like to modify their weapons, however, once a permanent modification has been made, or if the weapon has been taken apart outside of expected maintenance (Such as Pistol Cleaning, or Barrel Cleaning). 
  • Stripping a Weapon Completely during Cleaning
    Typically, stripping and cleaning a pistol only entails splitting the Slide and Frame, and cleaning the Barrel, wiping dirt from moving parts and applying fresh lubricant. Removing parts, such as the trigger mechanism, and damaging them is concidered user error.

    Typically,  stripping and cleaning an AEG / Gas Blowback Rifle entails removing the inner barrel for cleaning. Any further work, such as Gearbox Maintainance, should be carried out by our Shop Technicians.

    For further help on maintaining weapons please free to call us on 01484 644709.
  • Use of Poor Quality BBs
    Please don't use Cheap / Low Quality BBs in Airsoft Replicas supplied by us, if we find evidence that low quality BB have been used we cannot accept a return. Unfortunately,  more and more RIFs booked in to our workshop with damage caused by a poor choice of BB. Poor quality BB’s are BB’s which have been manufactured in a location with poor quality control, resulting in ammo which breaks easily, has mold lines, injection marks or poor weighting ratio. We recommend using BBs supplied by: ASG, G&G, King Arms, BB Bastard, and Amoeba. If we feature the BBs on our website they are safe to use with your Airsoft Weapons.
  • Damage by Dropping, Force Damage and Debris
    Although Airsoft Guns are typically built and designed to last they are Toys, and are not manufactured to the same quality as Real Firearms. As such, dropping, hitting, throwing, and dipping in mud can cause permanent damage to Airsoft Replicas. We cannot accept returns of weapons that have been obviously mistreated, with parts missing and broken.
  • Use of the incorrect Charging unit
    Please ensure that when charging batteries the correct Charging unit is used. For example, do not use a Li-Po Charger to charge a Ni-Mh battery, or a Ni-Mh Charger to charge a Li-Po Battery. Please read all supplied instructional material, as we cannot accept the return of items damaged in this way.
  • Use of 11.1v or Higher Li-Po Batteries
    High Voltage / Discharge batteries can cause permanant damage to AEG internals, please see the section below for further infomation.

Returns Related to included Free Chargers / Batteries

Unfortunately we cannot accept returns of Batteries and Chargers that comes supplied in a bundle with a weapon as these are considered free gifts and are typically of a lower quality than other available chargers and batteries. For example, batteries supplied for free with weapons usually features a low mAh rating and feature a low charge capacity.

We recommend that when purchasing an Airsoft Weapon you also purchase a new Battery and Charger (if required) for maximum reliability.

Two Tone Service 
For more detailed Terms and Conditions please see our Two Tone Service Terms and Conditions Section.

Frequently asked Questions

What is your returns period?

Our returns period is 14 days from when you initally recived the item, if you no longer want the item you can return it to us with the origional packaging. However, we will be unable to refund your postage.

How long is your warranty period?

The warranty period for all items we sell is one month from the reciept of your product. We can replace your product if was recieved damaged or broken through normal use, but not if it was through user error. If the item is found not to be damaged through user error, we can refund your postage. Please contact us to discuss replacement or the fixing of your item. 

How do I arrange a return?

To arrange a return please contact us via Telephone and we will talk you through the steps required to return your items. This typically means filling in a returns form and posting it back to us. If the product is faulty, you will recive a refund for the cost of your post.

How do I get a returns form?

To recieve a returns form please contact us via Telephone and we will E-mail you a form to print out and fill in.

Who should I use to post return items?

We suggest that you use Royal Mail 2nd Class Tracked, as it allows us to tell how much you have been charged.

Can I cancel orders which have not been dispatched?

You can cancel any order that has not been dispatched. Please call our Customer Care team on 01484 644709 between 9:30am and 5:00pm

What is your returns address?

Patrol Base Limited, 
Unit 5 Dale Street Mills, 
Dale Street, 
HD3 4TG. 

How can I contact you?

You can contact our order processing department using the following options:

  • Telephone: 01484 644709
  • E-mail:
  • E-mail:


We successfully complete 99.4% of all orders within 24hrs of being placed, providing you items are in stock! Next WORKING DAY delivery gives you free tracking updates which can be sent via email or text so you are not waiting in all day. To receive full tracking details and updates please provide a correct mobile phone number to all your orders and an up to date email address! 

We deliver to most places in the EU, for more information please see the "Where do you deliver to?" section below.

If your item has not been delivered within 24hrs of choosing NEXT WORKING DAY delivery please contact our store ASAP on: 01484 644709.

Frequently Asked Questions

How can I contact you?

You can contact our order processing department using the following options:

  • Telephone: 01484 644709
  • E-mail: - General Inquiries - Adam, Shipping Deparment Manager - James, Returns Department

What is the cut-off point for next working day service?

The cut-off point for next working day service is 2:45 PM, please order before this time to ensure we can process the delivery before our courrier arrives.

Is Saturday delivery available?

Yes, we do allow for a Saturday delivery, however it is costly. A standard saturday delivery can cost between anywhere between £35-£50 plus dependent on location and weight. Please contact us beforehand so we can arrange a price for you.

Which Courrier do you use?

Our main courrier is UPS, however we do also use Royal mail for deliveries where postage paid is under £4, not next-day and with an order value under £20. 

Do you deliver to Northern Ireland / Scottish Highlands / Channel Islands?

Yes we do deliver to Northern Ireland, the Scottish highlands and the Channel island, however we cannot offer Next Day service to those locations and may require additional postage cost. If an additional postage cost applies to your order we will contact you via your supplied phone number or email.  

I am ordering Krylon Spray Paint, what special rules apply to the postage of these items?

When ordering Krylon it is important to note that we cannot ship fewer than 4 cans outside of the UK, and less that 2 cans to Northern Ireland, this is due to rules for transportation of pressurised containers with our courrier service. 
We also cannot ship Krylon to non-EU countries. We apologise for any inconveniences caused.

How do I track my pacrel?

If you order was sent via Next Day Service using Interlink you will recieve an E-Mail from them with tracking details and estimated delivery time. If you did not recieve this email or cannot find your tracking information please feel free to contact us.

Where do you deliver to?

Outside of the Mainland UK we deliver to the following places:
Please note that if the delivery location is outside of Mainland UK we cannot offer a Next Day Service

  • Andorra
  • Austria
  • Belgium
  • Bulgaria
  • Channel Islands (Guernsey / Jersey)
  • Czech Republic
  • Denmark
  • Estonia
  • Finland
  • France
  • Germany
  • Greece
  • Holland
  • Hungary
  • Italy
  • Latvia
  • Liechtenstein
  • Lithuania
  • Luxembourg
  • Monaco
  • Netherlands
  • Northern Ireland
  • Norway
  • Poland
  • Portugal (Excluding Azores and Madeira)
  • Republic of Ireland
  • Romania
  • San Marino
  • Slovak Republic
  • Slovenia
  • Spain (Excluding Canary Islands Ceuta and Melilla)
  • Sweden
  • Switzerland

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Need Help? Call a specialist on 01484 644709

Monday to Saturday 9:30am to 5:30pm, but don't forget our late night Thursdays 9:00pm closing!

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