[Bullpup GOD]

Hey guys! I am getting back into airsoft after a 2 year break, and i'm getting into teching now. I'm attempting to fix up an old M4 i have before i sell it. I am attempting to remove the upper RIS from the gun, and have had no luck. It is a JG/Matrix M4-16 Zombie KIller. THe RIS is rather odd. THe lower ris comes off quite easily with a few screws, but can't seem to get the upper half off. It seems to be threaded on, and i attempted to turn it, and got a 1/8th inch turn on it but it's not budging. I now can't turn it back towards the original position. Here is a picture of the gun:

As you can see, it does not have the standard locking ring. Any ideas on how to remove it? I have not seen any other ways it could mount on. HAve not seen any sort of RIS like this. Also, when removing front flip up sight, there is a metal rod connecting it from the upper reciever. That is something else im trying to acheive, but that can be done at a later date.
Also, if interested in buying, here are specs

Matrix 3000 Torque motor
Irregular spring, roughly M117
Custom Metal Piston Head
High Torque Gears
MOSFET
Local area only. Meet up at Power Ops Airsoft.

 

[Hangtight]

The metal tube connected to the front sight/Gas block is the dummy gas tube. It should pull straight out unless you've tried to twist the hand guard off with it in place, in which case it could be kinked at the receiver end where it passes through the barrel nut.
To remove the hand guard, take out the Allan bolts that are holding it to the adapter at the receiver end. You will then be able to see the barrel nut. If you've wedged the adapter by trying to twist it off when attached to the hand guard you will now need a proper AR armourers tool to remove the barrel nut and free the adapter.

 

[Bullpup GOD]

The metal tube connected to the front sight/Gas block is the dummy gas tube. It should pull straight out unless you've tried to twist the hand guard off with it in place, in which case it could be kinked at the receiver end where it passes through the barrel nut.
To remove the hand guard, take out the Allan bolts that are holding it to the adapter at the receiver end. You will then be able to see the barrel nut. If you've wedged the adapter by trying to twist it off when attached to the hand guard you will now need a proper AR armourers tool to remove the barrel nut and free the adapter.

Sorry, dont mind the second pic, different variant. Where might the allen nuts be located? I do not see any in the front end of the receiver.

 

[LightIsRight]

If you look at the end of the rail close to the magwell there are some cylinder shaped objects on the rail. Look there.

 

[Hangtight]

They will be a barrel nut, and there will be something clamping the hand guard onto it. Lost some pics with the lower RIS removed and let's see if it can be figured out.
Got the gas tube out?

 

[LightIsRight]

Wait, which one is it? The gun in the second picture has a different rail system than the first and last ones.

 

[Hangtight]

Helpfully, it's not the one in the second picture...