MaxxPro Installation Tips

MaxxPro Installation Tips

MaxxPro Installation Tips

In this article, we are only considering the effects of your magazine, tappet plate, tappet spring, air nozzle, and Hopup unit.

There is no guaranteed fitment with all rifles and that is why we are writing up some tips that will help you install this HopUp into your rifle. These modifications and tunings can help with any HopUp but we learned that these will help you to install your MaxxPro.

M4/V2 Compatibility


  • All HPAs
  • G&G
  • King Arms

Modifications required

  • Krytac may require trimmed tappet spring
  • G&P requires fitment (i5 not tested)


  • VFC requires 21.4mm Nozzle or tappet/-spring modification (see below)

Not Compatible

  • KWA (maybe the new ones; let us know!)
  • ICS requires special model

The MaxxPros have great air seal, but depending on your setup may cause feeding complications which can be resolved by tuning your nozzle and tappet plate spring. There are multiple kinds of buckings and here at Umbrella, we classify them by their shape and the length of the bucking's lips. This is important since we can use this to determine the perfect length. Generally, long bucking lips require short air nozzles, and short bucking lips require longer air nozzles. Deviations from the perfect length will cause a plethora of problems and you can use this guide to identify which tricks will help you.

In case you are looking for a great flat hopped bucking check out our MadBull Blue Flat Hop (Short-Lip) Buckings here: {LINK}

Case 1 - Horrible Feeding / Consistent FPS

This can be resolved by using a slightly shorter air nozzle, spacing the HopUp further away from the gearbox. Generally, we recommend a 21.4mm in combination with our Madbull Blue (link above). 

Wondering why we are using 21.2mm VFC Air Nozzles in our OCAWs? 
We shave the front the tappet plate by 0.3-0.5mm to allow the tappet plate to move forward further inside the Gearbox. Though not required for guns below 35RPS we still think this is a best practice. 

Case 2 - Inconsistent Feeding and FPS (maybe even jamming)

The tappet spring is most likely too weak. Trim the tappet spring by two coils and fold over two to recreate the mounting loop as shown in this photo.


1. Own Bucking
If you are using your own bucking in the MaxxPro, there is a chance that it will be too tight causing jamming and feeding issues.

2. BB Rollers or Low FPS
After firing in semi-auto you may experience a BB rolling out of the barrel, because the Air Nozzle pushes the BB past the bucking lips and the R-Hop, without the piston having been released. Likely due to the tappet spring being too strong or not enough hop being applied. 

Weekly Question

Which barrel lengths should we add to our inventory? Comment below!

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