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Discussion Starter · #1 ·
Ok ladies and gentlemen, since my skills in the area of troubleshooting have run out in this project, I am now turning to you, the awesome people of this forum.

For almost a year now I've been dreaming of a G36 DMR. When i finally got all the outer parts that i need and what i thought was some decent internals, everything started failing.

Firstly the Selector plate busted so i got a new of those. Then the microswitch i had in the switch-assembly broke, so i got a brand new switch-assembly and it shot fine. Then i started having troubles with feeding. No idea what it was, but that's gone now.
While trying to redo thw wiring, i managed to cause damage to the mosfet that was attached.

My current, and most alarming, issue is that the gun fires around 60M/S (~200FPS). I've checked the gearbox and all the compression is working fine. No leaks at all.
I've chekced the hopup-chamber too and that thing is also totally air-tight.

The only thing that remains (AFAIK) is the connection between GB and Hopup.

SO, my question to all you skillful modders is this: How do i stop that leak?

Here is a picture of my creation:


Externals:
*CA G36C body
*CA G36 stock (the long one, not the one for C)
*CA G36 long handguard with bipod
*G36 outer barrel with another 10cm (K-version) outer barrel added for extra length
*Random mock suppressor filled with jute rolled around an AEG-spring (Best way to make a working suppressor i've ever seen)
*Modified G36-rail to look more like KSK-rail
*ARES short 20rds magazines (SO AWESOME!)

Some sort of scope will be placed on this and i also would like a cheek-riser, but we'll see what happens.

Internal parts:
*Guarder or G&P gears (normal ratio)
*SRC Piston with 5 metal teeth
*M120 spring
*SRC Ultra Magnetar High Torque motor
*Unknown pistonhead (ball bearing though)
*Ball bearing plastic Spring Guide
*Ball bearing bushings
*Unknown metal cylinderhead

If anyone got any suggestions, i'm all ears. :)

(Yes, i know that this is a bed-picture, but at the moment that's all i got)
 

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What brand of bucking is it and also did you check the compression with the nozzle all the way back? If so there may still be a leak there, but its probably an airleak either between the barrel and bucking, bucking and nozzle or possibly both.
 

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Discussion Starter · #3 ·
I've tried TM original, PDI w-hold and Guarder (the clear one).

Ithink i have tested compression with the nozzle both in back and front, can't remember right now.

The is no leak between bucking and barrel, i'm certain of that as i have tested it.


I will try with the nozzle at the front tomorrow. Thanks for reminding. :)
 

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When testing compression parts you always want to make three checks

1.check the cylinder for leaks by compression testing it without the nozzle.

2. Compression test again,this time with the nozzle on

3. Place the complete cylinder assembly in the GB and install the tappet plate spring.This will naturally force the air nozzle into its furthest forward position.Compression test again.

If you have ruled out all variables in the GB,next make sure your getting no leaks from your bucking.I use an Anaerobic gasket maker(seals in the abscense of oxygen)on my inner barrel where the bucking would be installed.A thin film is all thats required.After applying I then install the bucking.As an added security measure,and to ensure no air gets between the bucking and outside of the inner barrel I whip the bucking with dental floss.This method completely seals the bucking to the inner barrel.

Reassemble everything and chrono test.If the result is still dismall,you will need to either A.find a nozzle that will seal better in your hopup,or B.mod your air nozzle.I have heard nail polish applied to the smaller diameter end of the air nozzle is good to use to increase this portion of the air nozzles diameter and create a better seal.I have tried nail hardner and while it does work,its not very durable.I have been experimenting with spray on polyurethane,and am getting some good results.I have been spraying on a coat of polyurethane holding the can 10cm or so away from the nozzle and turning the air nozzle as I sprayed.After an application I hold the nozzle straight up and down while turning it to ensure the over spray is uniformally dispersed around the air nozzle,then set aside to dry completely.
I apply three coats,and after the third has dried sand the air nozzle smooth with 300grit emery cloth.You will want to build up the outside diameter of the air nozzle to where it just fits inside the hopup.
 

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Discussion Starter · #5 ·
Right, small update to my old thread, if anyone is interested. :)

I hadn't done anything to this rifle for a few months as i got myself an M14 DMR to have some fun with. However, i found that the M14 DMR was quite heavy at the front and that my left arm is not quite strong enough to lug that sexyness around. So i thought i'd have a go with some of my G36s (yes, i have several versions of that gorgeous thing).
I put this one together and it still only did around 50-70 M/S (165-230 FPS). So i fiddled around some with different front units (the thing that holds the hop-up unit and inner barrel) and differen combination of hop-up unit, barrel and bucking. I finally found a combination that works! It now does around 100 M/S (328 FPS). :D I'm extremely pleased with these results as it actually allow me to use the gun in games, even though it doesn't shoot very hard or far. It does however shoot quite good at around 40-50 meters. All i need to update now, in order to increase the FPS, is the spring as i assume that the current spring is a bit crap. I have a few harder ones laying around and i know for a fact that i have a 140-spring in my M14, which i will experiment with.

Also, the externals have been changed slightly since that first picture was taken. I will try to get a woodland photo of it this weekend, as i plan to get out for some weekend fun stuff.


Like said before, not sure if anyone was interested, but i thought i'd update the thread since stuff have actually happened since it was created.
I also want to thank Uller for the extensive reply. It helped! Without it i wouldn't have continued to try with this project.
 

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From what I hear, the G36's have a weak selector plate. It typically the first thing to go on the gun I am told. Even though it is hear-say, it you might want to be prepared for that.
 

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Just so your aware theres a fairly common fault with the hop unit on G36s as they sit about 1mm to far forward to make a good seal on the nozzle/rubber.

You need to remove some material from the 2 'ears' that stick out from the back of the hop unit, the 2 lugs that twist into the hop holder and from the top/front screw of the gearbox case.

It also wont hurt to stretch the spring that pushes the hop unit against the gearbox aswell, so it pushes back that little bit harder.

Don't go to wild or you'll suffer feed problems, but it can be sorted by fitting a sector chip to extend the throw of the nozzle/tappet.
 

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Discussion Starter · #9 · (Edited)
Thank you Zero! I agree. :D


@Libelle
You are quite correct. The Selector Plate on the G36 brake very easily. I've had 2 brake on me the past year, both in the same spot.


@Vindicareassassin
Indeed, the hop-unit is quite troublesome. I used to try to fit a metal unit to this rifle, but after finally finding a plastic unit i filed it down about half of a millimeter. Might need to file it slightly more though...

Thanks for the tip on using a stronger spring! I'm gonna try to create a small spacer to put between the spring and the unit to make it push a bit harder.


EDIT:
I just realized something. Filing the hop unit is not going to do a damn thing... The hop have these hooks in the front that hook up to the front peice so no matter how much i try to push the unit backwards, it's gonna be in the exact same position no matter what happens. :D

Doing that thing with nailpolish on the nozzle might be a good idea...
 

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Discussion Starter · #11 · (Edited)
@chiba
Yup, thought about that the minute i woke up this morning. :D
I remember doing that to my M14. But fact of the matter is that i really don't want to open this gearbox up... Guess i'm gonna have to anyway, to swap springs...

Thanks for the advice. :)

@Vindicareassassin
I must been toot tired last night to understand you... Now when reading your post again, i understand which "ears" you mean. :D You must've meant the FRONT of the hop-unit, not the back, because now i see how that would help. :)


EDIT
WOOHOO!!!
It's now doing 145M/S (475FPS). :D

I filed on the tappet plate and the ears on the hop-unit, as vindiassassin suggested, which made the gun do 110M/S (360FPS). Then i put in my m140-spring and it's now doing brilliant.
Now i can finally justify having it SEMI only and can actually call it a DMR.
I might try to get it up to 150-160M/S (490-525FPS), but for now this is great.

I will try to get some proper pictures this weekend. Thanks to all that helped, you guys rock!
 

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Vindi really knows what hes talking about when it comes to the G36 platform :) here is also my 2c from my G36 DMR build since it sounds like you were having some of the same issues I had in my build.

(This is right when I got the SL9, so everything has changed since this picture)


I traded PMs with Vindi a while ago about a feeding issue, at the same time I was having simmilar FPS issues.

The symptoms: I was having random double feeds/no feeds. FPS would stay steady around 420FPS for a while then drop off and dribble for a few rounds, and then jump back up.

The solution was a combination of things:
1. Replace the stock tappet plate and selector plate. They break/bend a lot when in use especially as they warm up. I can't remember which selector plate is in there right now, but it's red. And I got a few back ups at the same time, but the red one is awesome (King arms comes to mind, but I'm not sure). My replacement tappet plate is a Modify, amazingly stiff and solid, which is necessary for one of the modifications.

2. Get an AUG nozzle. The right AUG nozzle is just a hair longer than the G36 nozzle and helps with the GB - Hop-up seal.

3. Sand down the front of the tappet plate and glue the nozzle into place. This is covered in Vindis DMR guid and will give you that extra little bit to make a good seal. Basically the cross section should go from : -^- to -^ ; if that makes sense.

At this point you should have more than enough to solve the seal issue, especially if you stretch the spring and cut the "ears" as others have previously mentioned. Now for feeding issues.

If you put the MB together and hand cycle the nozzle you see that there is a step on the tappet plate that causes the nozzle to stutter as it feeds... IMHO that leaves enough of a pause that, on a full magazine/wound up high-cap, will force additional BBs into the chamber. Sooo...

4. Modifly the tappet tab... here are some pictures:

Standard set up:


Do this:


To get this:


By cutting it at that point the nozzle is sitll pulled back more than enough to load a BB, but is released forward with more force and earlier in the cycle. The additional force on the tappet plate combined with sanding down the front of it are the reasons you need to make sure you have a really good quality tappet plate. The additional force will break/deform the tappet plate if its the stock one. If posisble find one that is not glued together. i.e. doesn't have a joint where the tappet plate comes up to hold the nozzle.
 

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Discussion Starter · #14 ·
Ah, i'm not sure if i mentioned it or not, but i don't have an issue with feeding on this rifle. At least not yet. :)
And after doing the "ear-mod" on the hopup-unit, the issue with low FPS has been reduced. Might need some more filing to get it perfect, but as it is now, i'm quite happy.

I'll be going to a game tomorrow to try this baby out.


Regarding the weak selector plate: I went around this problem by completely removing it. Since this is supposed to be Semi only, there is no need for the selector plate. The safety is engaged by the fire selector and since the cut-off lever never needs to be disengaged, the selectorplate is obsolete. What i did instead was to solder a small peice of stripped wire between the tinplates from the Switch Assembly.
 

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Regarding the weak selector plate: I went around this problem by completely removing it. Since this is supposed to be Semi only, there is no need for the selector plate. The safety is engaged by the fire selector and since the cut-off lever never needs to be disengaged, the selectorplate is obsolete. What i did instead was to solder a small peice of stripped wire between the tinplates from the Switch Assembly.
Yeah, I have done this to my SL9 box since I have since converted my G36 back to a G36c with a M4 length barrel and the standard carry handle, worked out really well. Let us know how it works out, I haven't done any mods to the actual hop-up unit so I'd be interested to hear how it works out. Although I have been going down the dark road of custom building so it may be a moot point for me...
 

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Discussion Starter · #16 ·
Right, was supposed to report back regarding this weekend.
So the rifle performed excellent. Decent range (50-60 meters) but the spread was a bit much. Might have been due to the weather. It was rainy as heck. xD But i will test the rifle in dry conditions too at some point, just to get a reference.

When cleaning the rifle from dirt and water, i saw something i hadn't noticed before; the cylinder has a quite big port. I'm not sure if i should replace this cylinder with another that i have, which has a smaller port and is slightly further back. Is it worth trying?


Anyways, i'm happy with the rifle, it performs just as well as i had hoped.
Sadly, most of the magazines are rubbish and don't feed properly (i know it's the magazines and not the tappetplate since some magazines work fine) so they need to be lubricated, but i have no idea how to fix that. Anyone got any suggestions or links to guides i have not found yet?


Sadly i forgot my camera at home so i didn't get to take any pictures of the awesomeness. :(
 

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It depends on your barrel length as to the cylinder you run.

If your barrel is 450mm or longer you should really be using a full cylinder, 1 with no ports or holes, to provide enough air volume for the barrel.

You shouldn't use any lube on mags as it transfers to your hop and will cause in-accuracies. your best bet is to drop the spring out and stretch it, to force to BBs out with more pressure, but it will eventually revert back to how it was over time.

Or if your willing to loose a bit of BB capacity you can also fit a spring pre-load spacer in the mag, which achieves the same thing as the spring stretch but it wont loose the power over time.
 

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Discussion Starter · #18 ·
Well, i'm not sure how much i can fiddle with the mags as they're not really mine. I'm borrowing them long term from a guy in my team. He suggested to lube them up to get them to feed properly, but i guess i can try to sort that spring out. Thought they're only 50rds mags. xD


Regarding barrel - cylinder volume; i actually have no idea how long my barrel is, nor how tight it is. :S
But i think it's a 509mm * 6,02mm. Too bad i don't have a full cylinder laying around... Might have one in another box, if i'm not mistaken... I'm gonna check on that tomorrow actually.

Thanks for the tips! Much appreciated!
 

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I'd just do the spring stretch then, as that doesn't damage or alter the mags in any way.


Its worth fitting the full cylinder if you have 1, it will help shift along a heavy BB much better, it sounds as if the cylinder you have fitted is for a G36C with its short barrel..... ideal for firing .2s if thats your thing :hehe:
 

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Discussion Starter · #20 ·
Right, i put in the full cylinder. Didn't do any difference at all. xD The chrono still shows 145M/S with .20bbs and 127M/S with .28bbs. I'm thinking of going up to my .36bbs. Only problem is that they're brown and almost impossible to spot so seeing how accurate they are is going to be touugh.

I should also try to get another scope as i feel that my M3 is abit too much...
 
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