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andrew321 October 15th, 2010 20:16

Kjw gbbr leaking magazine guide
I’ve seen a lot of newer players with the KJW M4, I figured I’d put something together for anyone venturing in taking their mags apart.
Might save a few “Help Me” posts!

This guide will show you the simplest way to fix your leaking KJW GBBR magazines. Out of the 11 magazines I have, only 2 have shown signs of slow
leaks. That’s not bad for being over a year old! They seem to be very well constructed, and sealed up tightly.
I’ve done some testing, and this method seems to work very well, and (so far) seems to be holding up.
I thought I’d
put together a guide of what I was doing, seeing as how many people seem to be picking up the KJ system.

Few things to note:

-Be cautious removing and replacing screws and parts. Do not strip or cross-thread anything.
It’s a long wait to replace ruined parts.
-Be very gentle with/around the O-rings.
They need to be immaculate to make a proper seal.
-Only disassemble to what’s needed.
If your Fill valve is leaking, then don’t tear the whole thing apart!!
-Take mental note of how things come apart. This will help you put it together.

-Medium sized Flat head screwdriver
-5/32 Metric Allen wrench
-Silicone Oil!
-Silicone grease

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STEP 1--------------Identifying the issue
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This is a simple, but also extremely useful trick I picked up from someone on these forums (Coachster?). Slow leaks can be hard to detect, and hard to gauge the rate.
Put the FILLED magazine in a sealed Ziploc bag. For prolonged storage, I store all my mags in a sealed bag, which quickly identifies leakers, and also keeps your house from smelling like a hockey rink.

If it stays deflated, then there's no leak. If it inflates over a week, it’s an extremely slow leak. If it inflates in a couple hours, well, keep reading!

As you’ll see later, the KJ mags tear down to three main parts, each with its own mating seal. To identify where the leak is coming from, use this old tire-repair trick. This will save you from tearing down the whole mag for nothing. And trust me, when you are re-assembling, you’ll see it’s worth it! Fill the container with water, submerse the Mag, and the bubbles will show you exactly where the leak(s) is.

================================================== ======
STEP 2- Disassembly
================================================== ======

Start by making SURE all the gas is vented out of your mag!
After that’s been done, notice on the base of the mag, there is two parts, the Fill Valve, and the Body Screw. First, take a flat-head and remove the Fill valve. Put it aside in your parts container.

Next take the 5/32 Allen wrench and loosen the Body Screw. Pull it out. It may require additional unscrewing when it’s 80% out. It’s a long screw! Remove the crush washer on the screw, and put it in your parts container.

Now, the bottom third of the body will come loose.

Move the BB Tube out of the way, and pull the last two Body thirds apart.

So you should now understand how the KJW M4 Mag tears down. I’m not done playing around with the Upper part of the mag, so that will be updated as time goes on, or if someone wants to input their wisdom.

================================================== ======
Step 3- Fixing
================================================== ======

Here’s what I’ve seen for leak causes so far:
-Debris on O-Rings/ Mating surfaces
-Dried out seal/ Worn out seal

First off, you’ll need to remove your O-Rings from the Body. They are stuck on there tight, and require a little caution getting them off. Take a small flathead (or better yet, a blue plastic “safety multi-tool”), and your fingernail, and lightly pry, until you can get under it and pop it off. Also, cutting off a piece of sour-cream-type container works wonders! Take a clean rag, and gently wipe it clean. Put them aside in your parts bin.

Now, take the following 4 parts out of your parts bin, and place them in a small container/jar. Fill it with as much silicone oil as is necessary to coat all parts. I have had 100% luck so far with AI grenade oil. It’s not the cheapest to pour a whole bottle into a jar, but it WORKS. If you have a GBBR, chances are you can afford it ;). You can keep the oil container full for future leaks.
Let this soak overnight.

================================================== =======
STEP 4- Reassembly
================================================== =======

Fish out your parts from the oil container. Replace the O-rings and Crush Washer. SMALLER O-ring goes on the bottom third, LARGER goes on the other. ENSURE proper seating of O-Rings. Leave the Fill Valve aside for now. Here is where the Silicone Grease comes into the picture. Give your O-Rings a good coating, as well as the mating surfaces. This will ensure a good seal. Also make sure to Grease the crush washer before putting it back in. I use Sticky G, but I’m sure Super Lube, or similar O-RING SAFE grease would do the trick.

Now you’re ready to put it all back together. Put the Body screw through the bottom third, and re-connect the top two parts. Replace the BB Tube, with the slotted side towards the Inside. (DONT put it all together without this!). Then put the bottom third with the top two, again checking to make sure everything lines up.

Now...Here’s the fun part. Getting the four foot long Body Screw to find the tiny hole at the other end of the magazine. If someone finds a trick for doing this, please post it! I’ve managed to get all mine together without too much hassle, some in 30 seconds, and some in 10 minutes. Just fish around until it catches. If you need, take it apart to get an idea where it needs to go.
When it starts threading, slowly tighten it, making sure everything is connecting and lining up properly. Once it’s all together and tightened up TIGHT, go ahead and grease, then screw in the Fill Valve.

Once that’s done, you should have a good-as-new, sealed up Mag!

andrew321 October 15th, 2010 20:17

Reserved for MAJOR leak testing. (Gasket sealant!)

If anyone wants to add anything, let me know! Iíll put it in. Any comments, or criticsms, let me know!

Amos October 16th, 2010 02:57

Want a break-down of the upper mag?

I can do one of those things later on in the week :)

I've taken every piece of these guns down the the very last part :)

andrew321 October 16th, 2010 11:35

I had a feeling you might have. That will be great to add in!

bshantz October 16th, 2010 12:50

Wow great write-up! I was actually surfing forums for tips on my KJ Mag leaks and low and behold someone saved me hours of research!

Great stuff, as soon as I get home I am putting this to the test.

I have 6 KJ mags, 2 with slow leaks and 1 with a major(ish) leak.
Will be great to have these expensive magazines working again :P

cjboi October 16th, 2010 13:43

good job dude...

Ross December 27th, 2010 18:19

i've been trying to catch the body screw into the hole for two days now. *suicide

andrew321 December 28th, 2010 15:32

Welcome to hell. :)

I swear and curse everytime I have to get that damn screw threaded... Ive had the best luck keeping the lower section apart, threading it, THEN tightening it. You get a little more feel that way.

Amos December 28th, 2010 19:05

Haven't had a problem re-seating the bolts lol

It just takes some tinkering.

Ross December 29th, 2010 20:29

I did a weird mod in the magazine to guide it in. It worked for now.

JackAAA January 22nd, 2011 12:13

Hi, guys. I have a problem with one of my four magazines. It has quite strong leak from the exhaust valve. In order to solve this problem I need to disassemble the upper part of the mag, but I still can't do it :( Can anybody show me how to do it, please?

Olisharpeye May 16th, 2011 11:42

I am having the same issue as JackAAA, Leak in the upper part of the magazine. If someone could post a disassemble guide for that. Sorry if I get a little off topic here, but is anyone familiar with the hop up unit?

JackAAA August 8th, 2011 05:17


Originally Posted by Olisharpeye (Post 1467060)
I am having the same issue as JackAAA, Leak in the upper part of the magazine. If someone could post a disassemble guide for that. Sorry if I get a little off topic here, but is anyone familiar with the hop up unit?

Olisharpeye, usually the problem with hop up concerns in a stock hop up rubber. You should better buy a new one from ra-tech.:tup:

Jeff_Man October 29th, 2011 20:13


Originally Posted by Olisharpeye (Post 1467060)
I am having the same issue as JackAAA, Leak in the upper part of the magazine. If someone could post a disassemble guide for that. Sorry if I get a little off topic here, but is anyone familiar with the hop up unit?

Thanks for the awesome guide, it worked perfectly for me, my mag is working 110% now!

And As for the leak in the upper part of the mag, I had the same thing, so I put some drops of oil on the o ring inside the mag that is on the brass gas knocker (i dont know what else to call it) and now its working fine.

bean November 14th, 2011 17:58

Bump to see if any more info comes up on this and to see if Riley gets the upper section of the mag done. I want to tear down all of my mags and fix them up.

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