CO2 Mags for GHK GBB AR Box

[Greenmeance]

Evening Folks,

 

Just curious if anyone else has tried converting their GHK GBB AR Box mags to use CO2? If you have, did you just fill it with CO2 or actually swap the gas tubes out to take CO2 bulbs? Did it work or shred the box?

 

I'm curious because I happen to have a small pile of mags and a few projects in the works that would benefit from CO2 and I know the cylinders, valves etc inside some of the GHK mags have identical threads and outer dimensions, so the parts swap easily, but is it actually worth doing?

 

So that's this thing (it's a bit of a poor mans gbb I admit):

 

 

 

Here are the main blocks of the mags stripped down, GBB AR box left and GHK v1 CO2 left, as you can see the fittings are identical:

 

 

The CO2 tube screws onto the GHK GBB Mag part with no issues:

 

 

It would seem the only real difference is the outer shell and main block, gas routers and the fact there is no bolt hold function on the GBB AR Mags, even the exhaust valves fit properly:

 

 

So I can see this can be done and easily, but is it actually worth the trouble, thoughts?

[jv83]

I had the same thought but didn't have any co2 mags to test with. I used the GHK ar kit for a OA93 project since it doesn't require a buffer tube.It was a winter build and the temperature in Danmark only recently became gbb friendly så I have yet to test it properly. If I had co2 mags I could have done this months ago

I decided against trying to get a co2 mag to fit for several reasons, the main one being that I only use the gun for plinking and didn't want to spend any more money on getting a co2 mag just for butchering it, but also because you cant get spare parts for the kit.

 

Like you say, I do believe it could be done fairly easily and the gbb unit is quite simple in construction so it would probably work. The trigger unit is pot metal (although good quality)  so I would be more worried about it breaking after some use. If you do decide to try it you might want to upgrade the hammer spring to prevent light strikes and the recoil spring (the big one) to handle the extra force. 

 

If you do decide to try, let us know how you fare.

[DEVILHUNTER]

I'm pretty sure it will work (if the bolt carrier is strong enough) but you need some things:

 

Change the output valve for a CO2 one.

 

Change the fill valve for a KJW or drill the small hole it needs to be able to let liquid CO2 in (If you want to use paintball bottles instead of cartridges).

 

You can fill the magazine form a paintball bottle without the pressure regulator, or change one of the tubes to fit the cartridges.

 

If you search "devilhunter mod" you will find a better explanation.

 

By the way, the CO2 valve is easier to open than gas ones.

[Greenmeance]

jv83, spare parts are actually pretty easy to come by, apart from breaking down wrecks, Samoon and G&G both do every bit as spares:

 

https://samoon.com.tw/spare-parts/other-spare-parts/ghk-box-mg-spare-parts

https://samoon.com.tw/spare-parts/other-spare-parts/gbb-box-parts

 

Something interesting I found is that although alot of the parts are the same (aside from the G&G v2 bolt) there is a real difference in the cylinder bulbs giving different fps, basically bigger hole, more gas flow.

 

(High cylce left, GHK right).

 

G&G

 

The ellusive Samoon "High muzzle and cycling velocity Kit" turned out to be a rreally cut down cylinder bulb with a longer spring

 

 

I'm not too worried about the trigger mech, other than normal wear and tear there isn't alot of strain on anything than the valve knocker (firing pin) but lets see what happens.

 

What I am worried about is this part, it has some obvious stress points and wouldn't be easy to reproduce in metal:

 

 

 

 

DEVILHUNTER that's some good info! Mod 0 would work nicely in a finished version.

 

A weird observation though, I think these AR GBB Boxes might have AK exhaust valves in them, the stems are shorter than the ones in the GHK Co2 mags:

 

Left: GBB Kit, Centre: GHK CO2, Right: AK High Flow.

 

As alot of this is second hand, it's hard to know what's oiginal and what's been put in there. Reckon I've to see what fits with the box in a lower receiver.

 

The "bolt carrier" is just a simple blow off valve really, one solid lump of metal with vent holes/ports at the back:

 

 

 

 

Might pick up a refillable co2 capsule and test very very carefully before I try anything at decent psi.

 

[jv83]

Good info Green, I think you are right about the plastic upper having obvious stress points, maybe a stronger recoil spring or appropriately placed foam buffers might alleviate this.

I recall reading of someone using Action upgrade valves but I cant for the life of me remember which ones!

 

It also occurred to me, that the main block and gas routers for the co2 mag might lower the pressure when using 12g co2 bulbs, but its just a thought.

[jv83]

Ah just saw an old guide state that the action valve for the GHK AK fit perfectly in the gbb kits.

 

http://www.gtapex.com/08/airsoft_ghk_gbbar.html

[Greenmeance]

Ah just saw an old guide state that the action valve for the GHK AK fit perfectly in the gbb kits.

 

http://www.gtapex.com/08/airsoft_ghk_gbbar.html

 

Came across that really good in depth review awhile back, Endo the guy that wrote it actually sent me the pics from the High Speed FPS kit above, as I couldn't find one any place and he had one!

 

That's the AK high flow valve on the right, with the elliptical cut outs:

 

 

Looks like the Samoon/GHK CO2 exhaust valve is the same on GHK AK and M4 mags, with a longer knocker valve stem, can anyone confirm this?

 

ACTION also do this cylinder bulb, that looks like it might be made of a decent metal, for modifying of course:

 

[Greenmeance]

Has anyone (DEVILHUNTER) tried the normal GHK/Samoon exhaust valves with CO2 either m4 or AK?

[DEVILHUNTER]

Yes, I tried, they won't work.

 

You will need a extremelly strong hammer spring to open them, since because how they are made on the inside, the force needed to open them with the high pressure of the CO2 is quite a lot.

 

I got to open them using two hammer springs at the same time, but then another problem apeared. CO2 molecule gets into the rubber of the o-rings and expands and "dries" it. This is even more extreme when you have liquid CO2 in contact with the rubber, no matter if it is NBR or Viton. So when you shot, the front rubber will fly out or almost fly out and then get crushed. That's why CO2 valves have the white nylon seal on the front.

 

Trying to solve that I made my own pistons to use with the gas output valve bodies. Replaced the white seal with someones made by me with EVA plastic and PTFE. Well the valve worked but the need of a too strong hammer spring was too much for the bolt carrier to cycle.

 

So finally I decided I have to make a copy of the CO2 valves from scratch. I have 13 gas stanags I want to convert to CO2.

 

The CO2 valve you have there is from the first gen mags, new valves are more similar to the gas ones, Anyways they all have the same thread and external size so they are interchangeable. The only diference between the AK and M4 valves is the length of the piston as you have already seen. If the AR box valves have the same length of the AK ones, just get an AK CO2 from samoon, or cut a M4 one.

[Greenmeance]

Well got plenty of candidates for cutting! But since the AK co2 valves aren't expensive and this looks exactly like AR box valve, good tip DEVILHUNTER:

https://samoon.com.tw/spare-parts/ghk-ak-parts/gkm-11-4-co2

 

Just out if interest, are you filling your mod 0 mags at 850psi? Do you have any idea what the co2 caplets are filled at? A cursory google suggests about 800psi when sealed, obviously with the twin tube inside the mag that would allow some expansion and a drop in pressure. If I have that right.

 

Life is so much easier with a regulator! But no space for one this time.

[DEVILHUNTER]

You are having a misconception about how the gas (and CO2) magazines works, but don't worry, is very common misconception.

 

The cartridges are filled with liquified CO2. Whenever there is a liquified gas in a presurized container that means that the pressure is only function of the temperature (up to the critical point). It does not matter if it's the paintball bottle or the small 12g cartridges, this is called vapor pressure. Since liquids have much higher density than gases, we can store more energy in the same space.

 

Each time you shot, the gas (vapor in fact) in your magazine expands, making his work of propelling the bb and blowback. That means that now there is less pressure in the magazine, but didn't I said that pressure is only function of the temperature? Yes, so a small amount of the liquid green gas or CO2 vaporizes until there is again the same pressure on the magazine, thats what let us shot a whole magazine. If we had only vapor at 800psi with no liquid, you will get a couple of shots, like if you try to fill the magazine pointing it up, because there is no liquid to turn again into vapor and the pressure decrease very fast.

 

Well in fact I lied, it's not the same pressure after each shot. To convert liquid into vapor you need energy, where do you get this energy? From the vibration of the atoms, the temperature. So after each shot, the liquid gets energy from the magazine, which decrease the temperature of the magazine lowering the vapor pressure. That's what we call cooldown.

 

So I fill the magazines with liquid, like the cartridges do, but I fill them with more quantity than the cartridges have, anyways the pressure is the same.

[Greenmeance]

Good explanation DEVILHUNTER! So a slightly different question then given what you explained above:

 

How much liquid co2 do you fill your mags with? Hard to estimate i appreciate, do you simply time how long you are filling when not using a regulator? If I recall correctly the instructions of most gbbs say fill for a certain number of seconds.

 

From what you say, if you seriously overfilled (or completely filled) the mag with liquid gas there wouldn't be sufficent space to allow for the required amount of vapour and we'd start to get issues with the exhaust valves, venting, run away gun etc

 

All GHK mags I've taken to bits have two cylinders or chambers, pretending for a moment that the liquid gas (CO2 or whatever it may be) is only fed into one, the second chamber must act as an expansion chamber, allowing space for liquid to turn to vapour in enough volume to cycle the bolt and shoot those BBs. If I haven't misunderstood there is likely more than enough volume of vapour to cycle more than once even if no liquid remains.

 

In the reality it wouldn't matter which cylinder the liquid gas ended up in, between the two there is still a fixed volume as you can't compress a liquid.

 

What's got me curious is what would happen if you supplied gas/co2 via an external regulator and limited yourself to semi only, would both cylinders or a small expansion chamber actually be needed? I guess the crucical question is volume of vapour.

 

I'm jumping ahead a bit here but I have a certain project in mind where semi only isn't a problem and there is ample internal space for a small low pressure regulator and fixings.