There is something about metal AEG internal upgrades.  Personally I think it is the looks.  A company from Russia has been making some really shiny internal replacement parts and I just had to get my hands on some.

Before we go any further, please take some time to read the Disclaimer Page.  It is important to note that I am just sharing my personal experience, and the experience of others may be different from my own.  With that out of the way, please continue below.


For one reason or another you will eventually be wanting to swap out the internal parts of your airsoft Automatic Electric Gun, or AEG for short.  Be it to replace something that has broken or to tinker with performance.  There are a lot of choices out there to fit anyone’s need, and one such choice is Combat Union’s line of Russian airsoft parts.

Combat Union is an airsoft parts retailer and manufacturer from Russia.  They have an extensive catalog, of which includes this metal upgrade parts set for AEG compression components.

Combat Union Packaging
Packaging is simple and effective.

The compression parts in an AEG are responsible for channeling air, through a pneumatic action, to launch bbs at your targets.  They are composed mainly of a Cylinder Head, Cylinder, Piston, Piston Head, and Air Seal Nozzle.  Miscellaneous related parts include the spring guide and main spring.

In the early 2000s it was very common for parts to wear down due to high-powered upgrades.  The maximum legal bb velocity in our country is 550 feet per second (FPS) with a 0.20 gram plastic pellet, and before this ruling it was open fps for some time.  Increasing muzzle velocity was the answer to improving your effective range.  AEGs with powerful mainsprings were abundant, and with that trend came higher stress on the working parts.

With this in mind, Combat Union’s parts can be seen as either a direct replacement or durability upgrade to prolong the service life of your AEG, but as I found out, they are not exactly drop in replacements and could cause novice airsofters  looking for a quick fix, some headaches.

Cylinder Head

The cylinder head is very similar to other cylinder heads in the market.  It has a flat back unlike the concave ones that are matched with silent mushroom-shaped piston heads.  This means you have available surface area to easily attach a conventional Sorbothane buffer to help absorb impact forces.

Black adhesive squeezed from cylinder head
A bit of black adhesive shown to have leaked out from behind the rubber bumper.

The holes on the cylinder head that slot into a gearbox’s retaining tabs seem over-sized which introduce about a millimeter of rotational play in either direction on a standard version 2 gearbox.  These holes on the version 3 offering are only ever so slightly smaller.  I prefer that cylinder heads have a sung fit to the gearbox with nearly zero play.

Loose cylinder head
The Combat Union cylinder head will seat in the ICS upper, but there is considerable rotational play.

Without a snug fit the cylinder head will rely on a combination of the tappet plate and cylinder to position itself in place.

Cylinder and cylinder head assembly
Combat Union cylinder head on an old cylinder.

If you look closely at the nozzle tube on the cylinder head, you will notice that halfway towards the main body it is thicker.  This area has more drag and may need some sanding.

Air Seal Nozzle

The included air seal nozzle has a single o-ring to help with air seal.  Some stock air seal nozzles do not have o-rings and could be a source of FPS loss and inconsistency.  It has become standard to place an o-ring in aftermarket air seal nozzles and it can be seen that it is true for Combat Union’s offerings.

air seal nozzle rear view
The o-ring is a little flat in profile and I was worried it would leak, but it didn’t.

Piston Head

Overall the machining on the piston head is quite good.  Ports were finished off quite nicely which allow unhampered air flow to expand the o-ring against the cylinder walls during the push stroke.  Other manufacturers have been caught to leave this part unfinished and it is not uncommon to find material lodged inside these holes.

If there is one critique however, it is that the piston head itself is not tapered  and smooth enough compared to other options.  This plants a fear in my mind that it may catch one day and drag along the inner cylinder walls causing damage.

Spring Guide

The Combat Union spring guides do feel robust.  However, it is in need of consistency in the manufacturing.

Combat Union v2 Spring Guide
Combat Union version 2 spring guide.

In the version 2 and version 3 sets that I purchased, they included their respective spring guides which are differentiated in the anti rotational lugs or tabs found at their base.  The v2 ones are narrower while the v3 are wider which correspond to the holes they slot into in their respective gearboxes.

The v2 spring guide had considerable vertical play on the outer shaft, while the v3 guide bearings and shaft would grind when spun.

Notice the gap between the outer shaft and the bearing?

I was successfully able to disassemble the v2 spring guide by removing the head screw.  However, the v3’s head screw was on there incredibly tight and I was unable to loosen it.

Combat Union v2 spring guide disassembled
Spring guide disassembled

Piston Body

Early aftermarket parts were made out of poly-carbonate plastics and information about correcting for angle of engagement was not a widely known topic at the time.   We often found ourselves ending up with  broken pistons at the pick up tooth end.

Enter full metal teeth racks. Apart from the available full aluminum piston from Systema, companies like Deep Fire started releasing polymer piston bodies that had metal teeth that extended from the release tooth all the way to the pick up tooth.

Deep Fire early version aftermarket piston compared to an ICS stock piston.

These were more resistant to breakage even without fine adjustments, they also allowed longevity in high stress builds such as very high rates of fire.

Piston teeth and sector gear mesh
Factory prep on third tooth allows sector gear teeth to clear even after correction of angle of engagement.

The teeth rack of the Combat Union pistons come from the factory with tuning in mind.  The second tooth is not present, and the third tooth is shaved down slightly.  These are features techs would normally have to manually modify themselves and are not present in stock vanilla AEG parts.

The body itself is machined quite nicely.  Again, you can see the machining patterns and the finish is quite nice.

The back side of the piston is also ported in numerous locations to reduce weight.  This is great and all, but I feel that the weight that the heavy full metal teeth rack adds counteracts this advantage and throws a lot of that mass off-center.

The two I got also do not readily seat onto gearbox rails.  On a standard v2 gearbox they slot in but the fit is very tight and it cannot move.  This means you have to shave material off of the piston body rails to ensure they fit.

Has Potential

One of the joys of airsoft is the exploration of new offerings from old and emerging companies and I think Combat Union’s kit can be best described as an unpolished gem.

The base material and design is here but due to some inconsistencies you will be forced to make adjustments to make it work for you. Although not a problem for seasoned veterans, this might not be something some techies may want to deal with.

The thing that really caught my eye and appreciated was the attention to detail in their metal teeth rack found on their piston body which show that they are knowledgeable of the advancements in AEG tech work.  Overall there are three main concerns I want addressed.

One: lightening of the metal teeth rack, because although robust, adds much weight and nullifies the purpose of the beautiful porting meant to reduce mass.

Two: Improve tolerances in the assembly of the spring guide to prevent the outer shaft from having too much vertical play or experience binding.

Three: Resize the slots on the cylinder head slightly smaller for a snug fit on the gearbox to prevent excessive rotational play; and/or widen the space on the cylinder head wall where the tappet plate moves along.

In any case, it is not strange for airsoft products to encounter some issues that need revisions, and it has been in the nature of the aftermarket parts market to have variances here and there. However, we can also say that some kits require less work than others to integrate into our builds.  So to stay competitive there is a need to address these concerns that have been brought up.

If these three are addressed I think Combat Union would be a solid choice on my list of airsoft parts manufacturers.  The raw look of their machined parts just look so awesome!

With that being said, Combat Union is a relatively new name in the market as compared to the classics and I feel their products can only get better from here.

Initially the fact that they were Russian airsoft parts was reason enough for me to try them out. After feeling up the kits I bought from them I was pleasantly surprised overall.  In the meantime, I will be applying some adjustments and see how far I can take them.

– J4

Published by J4

I'm Julius the tinker! I'm the owner of the Hobby & Tech Warrior website. I'm a website developer noob, gamer, hobbyist, tinker, and dreamer. I aspire to be a digital nomad.

Join the Conversation

1 Comment

  1. I’m pricing the internals for an upgrade to a aeg Dragunov all internals are needed not the barrel

Leave a comment

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.