AGM M4 GBB problem/tune up

zerohamster

Ok so I got an AGM M4 GBB (WA clone) over at adverts and Id like to give it a bit of a tune up/make it skirmishable.


I also have a PMAG I got with it which unfortunately seems perform poorly with the gun with problems feeding/sometimes causing jams and venting which I would love to sort out too.

The gun was supposed to come with an NPAS kit which had supposedly been in the gun before and the guy insisted fits in the gun however Im pretty sure the NPAS he gave me is the WE version and wont fit.

This is the version that he gave me:
http://shop.ehobbyasia.com/ra-tech-n-p-a-s-kit-for-wa-m4-version-1-gbb-series.html

I went to install this the other day and just couldn't see anywhere it could be installed in the bolt carrier assembly so if anyone can shed light on this I would be very greatful.

The gun also came with the hammer lock uninstalled and he gave me the wrong pin for it so if someone has a hammer lock pin knocking around I would love to get one to install the sear. It is the pin in this picture:


The gun wasn't shooting very well in full auto without the hammer lock in (1 shot would be good,next would be about 1/3 the fps and some would fire in twos etc...) so I wanted to test the gun with the hammer lock in and made a make shift pin but even with the hammer lock in, the gun wont shoot semi but does shoot properly in auto (perfectly feeding and no inconsistant shots like before).
I tried testing the action of the trigger with the upper reciever off and it seems to operate in semi fine but with the upper receiver on and firing it will just shoot in the inconsistant way before.

I would appreciate any help I can get on this and any tips on upgrade parts from anyone.
Thanks in advance for any help or input I can get!

bluestripe93

Thats the WE version of the NPAS you have,

This is a WA loading nozzle with a NPAS built in, Its not as good as the RA-Tech one but will still work, or you can take out the NPAS set from inside and put it into your current loading nozzle
http://shop.ehobbyasia.com/5ku-plastic-nozzle-with-tool-adjust-npas-set-for-wa-m4-gbb.html

I'd recommend you to get a lighter bolt for it too, This Vltor one is very good Its about €40 inc shipping but its well worth it.
http://www.rsov.com/product.php?langId=1&currencyId=3&manufacturerId=10&prodId=3935&cateId=0

And a Co2 Mag would be a good upgrade too, It would stop the green gas venting when you fire it on full auto, but might bring the fps up a bit so you would need the NPAS to adjust the fps back down to under the limit,
http://www.rsov.com/product.php?langId=1&currencyId=3&manufacturerId=10&prodId=13605&cateId=0
I've got both parts in my AGM GBB M4 and they make a huge difference in performance,

Not too sure about the firing problems, but try to get a pin and then test it,
You can get a set here with the pin you need, the site has free shipping too,
http://www.ebairsoft.com/aabb-reinforced-spring-p-3110.html

What happens when you try fire it on semi with the hammer lock in?

zerohamster

Thanks for confirmation of that one, nice to know I was duped by the seller (other parts were for WE too like the Vltor charging handle and firing pin that were part of the ad).

If I was getting a bolt+npas would that do as I have the stock bolt in but it looks to be cracked slightly near the rear so I might replace it fully.

The Vltor one looks good and If I was to replace the bolt carrier+bolt+get an npas would you say getting parts seperate or as a whole assembly would be better?

Sorry I wasn't clear on what I meant by when it vents gas. Basically when the PMAG is in it seems to jam and lock the valve open thus venting the mag which as you can imagine is annoying considering the standard mag works fine. The PMAG will also fire and sound normal but will somehow not feed a pellet into the chamber some of the time which is confusing.

Thanks for the links, Im working on getting a replacement pin and there is a small kit on ehooby for €4 so I might get that if ordering other parts as well but wanted to see if anyone local had one that I could buy perhaps.

When I try fire it on semi with the hammer lock in (using temporary bar/pin to simulate the proper pin) it fires the same as when the hammer lock wasn't in (ie auto but 1 shot normal power then one really weak then two and sometimes it seems to shatter one). It has that type of behaviour with the hammer lock out or set to semi.
If I remove the upper receiver and set it to semi and then simulate the bolt travelling with my finger it seems to lock the way I imagine the mechanism should and requires releasing the trigger to let the hammer rise to firing position again but then again I amn't sure ofwhat proper operation should look like. Perhaps could the bolt carrier cause this problem does anyone know.

Thanks again for all the help and thank you bluestripe93 for the help and links so far, much appreciated.

bluestripe93

Just out of interest how much did you pay for it?

You can change the Loading nozzle, Bolt carrier or add an NPAS all separately depending on how much and when you want to spend on it, Or you can buy it all together but it might be more expensive, and I don't think the VLTOR bolt comes in a set,

Is it the stock loading nozzle or bolt carrier thats cracked?

The NPAS can be taken out of the loading nozzle I linked to and put into your current loading nozzle if you want to keep it or replace it later,
The stock loading nozzle is quite good and wouldn't need replacing unless it breaks, But definitely replace the bolt carrier,

You might already know this but i'll tell you anyway,
The NPAS goes inside the back of the loading nozzle, If you look at your bolt carrier there is a round clip in the gap in the middle, if you take out the clip the loading nozzle will slide out, then if you look at the back of the loading nozzle there is a small pin, take out the pin then you will be able to remove the inside parts and replace it with the NPAS

Still don't know what's wrong with your trigger set, Its hard to know without seeing it or anything,
Can you put up a couple of pics of the insides?

Try separating the upper and lower, and put an empty mag into the lower and put your bolt carrier in, put the back against the buffer tube and put the loading nozzle into the mag lip in the mag (So its in place as if the upper is on) and test out the hammer and trigger if it works and see if you can see any problems,

After that if its still not working you will probably have to take out your trigger set to check it,
Take out the selector switch and bolt lock,
Take off the anti-rotation links and tap out the 2 pins(Trigger,Hammer), Just take out everything from the trigger set (Trigger, Sear, Hammer, Selector, Bolt lock) and check it all

This is how it should all work, These are from a real M4/16/AR-15 but it works nearly the same as the WA GBB Airsoft M4




I'll put up a picture of mine and how it should work/look like tomorrow,
Hope it helps you a bit but its hard to know what's wrong

zerohamster

Traded a jg g36c (with badly feeding mag) and €235.

Im going to go for that Vltor bolt carrier and the 5ku aluminium nozzle bolt with npas I think.
I want to at least try replacing the nozzle with this one as I want to see if I can solve the feeding problems with the PMAG as well as not having a slightly cracked one but if it turns out to operate worse I will just stick the NPAS in the original loading nozzle.

I noticed today that if I use the PMAG (lower output) it will fire on semi most of the time correctly (but that mag seems to feed bad with the current nozzle/not enough force to put a pelled in the chamber) but on the original mag it wont fire semi no matter what.

It is the loading nozzle that is cracked at the back slightly but if replacing it then I wont have to worry about that.
Yeah when I had taken the bolt carrier/loading nozzle apart to "install:rolleyes:" the NPAS I figured out where the correct one should go but thanks for the info you have provided as every bit helps and it is also nice to have a second source confirm where it should be.

I tried what you suggested with simulating the bolt travelling back and forward and it seems to be operating correctly without gas so Im wondering could the hammer lock be slipping under the speed and force of the gas operation?

When I get a chance Ill strip the trigger set etc... and put it back together although from diagrams it seems like the things are in the correct place but just that something is slipping or not catching properly when more force is applied so it is hard to tell. Could the hammer be at fault? (will post pics as soon as possible)

Thanks again for your help and if you can manage to take a few pics looking down into the lower receiver I would be very greatful to be able to compare them.
Cheers!

bluestripe93

That would be quite a high price to pay for it,
What size is the pin you have in place for the hammer lock pin? If its smaller it might be lowering the hammer lock and not making it catch on the bolt,

A long wooden BBQ skewer stick fits perfectly into the hammer lock,
Maybe try that?


Can't get a good pic of the insides, everything is black inside it and is hard to see the different parts, This is the best I can do for now

zerohamster

Unfortunately yep it was pretty high in the condition it was in.
I have a VLTOR bolt carrier and a 5ku NPAS loading nozzle on the way as well as a new pin set and hammer with a roller bearing like on your photo so hopefully it will run smoother after that and will be a nice gun.

The makeshift pin (bar really) I used was nearly the same diameter as the realy pin should be but only just a tiny bit smaller enough that the bar could be inserted into the hole without too much difficulty but it wouldn't fall out when turned at all so I don't think that was the problem.

Thanks for the picture, I had it set up the same so Im not sure what could be causing it but when I get the new parts Ill pop everything out and rebuild it. Looking forward to getting the parts as hopefully it should turn out pretty cool.

Now I just need a few mags and I want to get a flip up front sight to compliment the MBUS sight I have and Ill hopefully get to skirmish it.

One last question, Do you use HFC134A or Green gas in yours? (with standard mags or what brand of mags?)

Thanks again for the help!

bluestripe93

I use GHK Co2 Mag's, they work better than the Green gas mag's in the cold weather and its easy to change the Co2 if it runs out of gas during a game

They cost more than green gas mag's but are worth it

http://www.rsov.com/product.php?langId=1&currencyId=3&manufacturerId=10&prodId=13605&cateId=0
€47 inc shipping