Improving Tanaka AICS and KJW M700 barrel installation method

Hi there!

Today we will be looking at the Tanaka AICS and KJW M700 outer barrel, and hop up chamber installation methods, and how to make them better. You probably ask Yourself “why?”, well the simple answer is – because both installation methods have their faults wit a negative impact on accuracy.

So first let me show You both stock methods, and their faults:


Tanaka AICS:


1/2 – holes for metal pins that secure the chamber in the frame
3 – rubber O-ring on a round plastic part that holds the outer barrel
4 – screw securing the chamber in the stock
5 – nut that secures the chamber and the outer barrel mounting piece


As You can see the chamber is designed quite well, with those two metal pins that secure it in place, thanks to a two pin design the chamber does not move up or down, even when the stock screw (4) is tightened… The worst thing about this design it the part number 3 – and that is the outer barrel mounting piece. The problem with that part is that, is doesn’t give a stable connection (the barrel is held in place only by a rubber o-ring), so the outer barrel is free to move, especially that it’s being attached to the stock by a single screw in the front, that causes the outer barrel to be dragged down, and bend the inner barrel with it.




KJW M700:


1 – hole for a metal pin that secures the chamber in the frame
2 – screw securing the chamber in the stock
3 – outer barrel installation nut


As You can see KJW has a bit different installation method, but unfortunately, it’s not better than the stock Tanaka one. The single metal pin design, lets the front of the chamber move up and down freely, especially down, when the stock screw (2) is tightened. The outer barrel installation nut (3) is a step in the right direction, but it does not hold the front of the hop up chamber, and because of that is can cause the inner barrel to bend (when the tip of the inner barrel is secured by the outer barrel, and the hop up chamber is dragged down by the stock screw)




My design: (Hannibal reference 🙂 )


1/2 – holes for metal pins that secure the chamber in the frame
3 – screw securing the chamber in the stock
4 – thread holding the outer barrel
5 – inner thread pulling, and securing the chamber
6 – inner barrel stabilization collar


So I went for a full aluminum HopUp Chamber (because the plastic ones in Tanaka and KJW tend to break, especially when the stock crew is tightened too much) , with a two metal pins for support and stabilization. Additionally the front piece now has a thread for the outer barrel instead of an o-ring (4), and its being screwed on the chamber (5), that gives me two additional stabilization points. Next I wanted to make sure, the inner barrel sits as firm as possible so I added a long collar with an inner diameter as close to the barrel as possible, thus it’s supported till the very end of the mounting piece.


Thanks to this design, my inner barrel does not bend, I got a full free float outer barrel, and all the parts are connected so firmly, that You can carry Your rifle by the barrel and nothing will happen 🙂

Here are some additional pictures:


The mounting piece is screwed on the chamber



When inserted in to the frame, the front piece becomes an additional support for the whole mechanism.



Tanaka AICS outer barrel – threaded to accept the new mounting piece




The outer barrel is screwed on the mounting piece, providing a very strong connection.

Well, and that’s it, no more wobble, or worrying about the inner barrel being bent, or the outer barrel moving because of some screws 🙂



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