Need urgent help with this

[CaptainH]

I have put a madbull shark fin hop up bucking in my JG SL8 with a lonex metal G36 hop up unit. When I insert a mag the gun wont fire with a mag. When I don't use a mag the gun will work. I don't know whats causing this or how I can fix it.

 

[RR01]

I doubt that the new hop rubber has anything to do with it, unless it's put in in such a way that the rubber is blocking the inner barrel. Have you tried taking out the inner barrel and looking down it from the muzzle end to make sure that it's not protruding too far into the barrel and jambing a BB in there?

As regards inserting the mag, are there any wires running towards the front of the gun, as the only really likely cause would be if the mag was pressing on a wire or contact on the gearbox and breaking the circuit. Other than that, I can't see any other obvious reason where inserting a mag will stop a gearbox from cycling.

 

[CaptainH]

I doubt that the new hop rubber has anything to do with it, unless it's put in in such a way that the rubber is blocking the inner barrel. Have you tried taking out the inner barrel and looking down it from the muzzle end to make sure that it's not protruding too far into the barrel and jambing a BB in there?

As regards inserting the mag, are there any wires running towards the front of the gun, as the only really likely cause would be if the mag was pressing on a wire or contact on the gearbox and breaking the circuit. Other than that, I can't see any other obvious reason where inserting a mag will stop a gearbox from cycling.

Click to shrink...

I will need to take it apart again but I was sure it was clear before putting it back in. With the mag it will fire a few shots upside down but when shooting it the right way up nothing will happen. I will check the barrel again like you mentioned.

EDIT: There doesn't seem to be anything down the barrel which may be blocking it.

 

[RR01]

Do you mean that the gun stops cycling with a mag in place (i.e. pulling the trigger has no effect on the gearbox turning over), or that once the mag is in the gun it will fire a few BBs before stopping firing any more BBs out of the barrel?

If it's the first case, then it will be a wiring or contact issue, in that no power is getting to the motor. If it's the latter case, then it may be that the inner barrel/hop unit isn't sitting exactly right in the gun, so that the mag cannot feed BBs properly. I had the latter happen to me on an M4 which I custom built from parts. For some reason, my preferred hop unit would not sit in the right place in the receiver and stopped the BBs from feeding, whereas a different hop unit, which looks identical, worked absolutely fine. It can be something as small as being a mm or 2 out of alignment which can make all the difference.

One other thing. You said you fitted a Madbull Shark hop rubber. Was this one of the blue ones? If so, they are a bit thicker than some hop rubbers and can be a very tight fit in some hop units. This means that the rubber can get distorted and not sit correctly in the hop unit, which can cause feeding issues.