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EVO – Downgrade? NOT!

We did something in reverse...

So today we have done something complete against the norm... Especially when this has been so carefully produced by the wizards at Action Sport Games (known more commonly as ASG) in Denmark. We installed an Anti-reversal latch into their Scorpion Evo A3.


So why does the EVO not have one in the first place? The EVO is finely tuned from ASG to not have overspin issues. This is necessary due to it not having an Anti-Reversal Latch in it, contrary to most other AEG's.

Why did you do such a thing?!?!

In order to push the CZ EVO to higher rates of fire and trigger response, an ARL function was necessary. Attempting so without an ARL in would result in backspin after every other shot or burst when making something with a significantly faster rate of fire. This could cause the gears to run backwards and hammer the back of the piston, something you really don't want. Especially on a custom higher rate of fire gearbox build.


It's been seen before that the steel rack on the piston can be forced out through the piston, through the piston-head and into the cylinder! (once again, this is only on modified gearboxes!) Furthermore, backspin could result in double feeds on semi. The gear will overspin, load a new BB, spin back, then load a new BB again upon the next shot cycle.

There is also a trigger response factor to it. When the sector position can rest half-cocked on the ARL, it is effectively pre-cocking. Not as extensive pre-cocking as specific systems like the Gate Titan or some AEG's without breaking, but enough to make a noticeable difference.

Installing an ARL (Anti-reversal Latch):

So, we are doing this for a customer who wanted a bit more ROF and efficiency from their EVO gearbox, doing this work will void your warranty. We firstly punched out the centre pin of a normal ARL latch. Instead of using the pin we just knocked out, we used the original screw. The ARL is then placed where one of the existing screws is inside the gearbox shell as seen in the photo. The gearbox shell was then cut on both sides to allow room for the ARL latch. You need to make sure that it centred right on the bevel.


Due to having a spring wrapped around it, it cannot be a perfect fit with the gearbox shell, and it is important that it has a good fit on the pin (screw in this case). The gearbox screw was screwed further into the gearbox and located in the right position. Then the screw head was cut down to fit the original screw hole further in, offering support on the top shell.

The result came out perfect!
The customer has since used the EVO plenty without any faults from this custom ARL. The nozzle sits consistently, being partially retracted between each shot.


It has enabled us to build an EVO with a higher rate of fire and better semi-response. Even with a DSG setup, a non-ARL EVO is limited in trigger response.

Want this done to your EVO?

Simply drop and enquiry email to: jeppe@patrolbase.co.uk

This blog has been brought to your by our workshop engineer, Jeppe.

Written by Karl, who has written a total of 202 posts.

Posted in Patrol Base News | 3 Comments

3 thoughts on “EVO – Downgrade? NOT!”

  1. James Kendrick

    Will you need to upgrade the gears, piston e.c.t when installing the ARL due to the higher ROF or will the current stock internals be able to handle the higher ROF?


    1. Karl Post author

      It completely depends on how fast you are intending to go. For peace of mind and reliability then its always a yes on 90% of AEG’s on the market.


  2. Plepis

    Hi there! I’m currently looking into getting an EVO myself, and since i do my own teching, and heard the shimming on these might not be so “top notch” and/or i might want to chance the gearset for something faster, i was wondering, how would one shim the pinion to bevel with such a big motor grip? Having issues with finding answers online, and i end up worrying about it.

    Any tips?


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