JAC MP5 problem

My friends JAC MP5 wasn't holding gas in the internal talk so we opened it up today to see what was wrong. I figured it was a bad O-ring. It turns out the peice that connects the internal tank with the BV system was messed up. The threads were too small so it could not securly hold onto the small internal tank. The tank actually bew out of the pistol grip almost hitting my friend in the face and going at least 10ft in the air. How do we get it to connect? Or, where can we buy a replacement part? Does anyone have one, or is there a place that sells used JAC parts?(cough cough ehihn)

here are pics to help you understand,

Originally Posted by G36fanatic...

My friends JAC MP5 wasn't holding gas in the internal talk so we opened it up today to see what was wrong. I figured it was a bad O-ring. It turns out the peice that connects the internal tank with the BV system was messed up. The threads were too small so it could not securly hold onto the small internal tank. The tank actually bew out of the pistol grip almost hitting my friend in the face and going at least 10ft in the air. How do we get it to connect? Or, where can we buy a replacement part? Does anyone have one, or is there a place that sells used JAC parts?(cough cough ehihn)

here are pics to help you understand,

i got the piece somewhere around here. If I can find it it's yours.

And no, odds are you aint going to find one easily. Can I have some pics of the tanks threads if possible. If those are damaged you will have to figure out a perma coil ordeal and do a lot of re threading.

Like said, just bypass the whole tank. It is a common place for leaks. Easy to do and will avoid all this in the future.

Unless he doesn't have a regulator.

When it blew off was it using green gas? or did he have it rig'd up and running external?

It was green grass. He has the peice that screws into the bottom of the tank to make it external. How would we complety bypass the tank? The peice that connects directly into the the actaul BV system only stays in cause it's being pushed on. How would you seal this off and pit a hose to it?

Also, he needs a mag. How much would one of those cost, and where would we get one?

I'll ask him to look at the threads on the tank, I don't remember then being damaged, just too big, and the in-between peice too small.

Originally Posted by G36fanatic...

It was green grass. He has the peice that screws into the bottom of the tank to make it external. How would we complety bypass the tank? The peice that connects directly into the the actaul BV system only stays in cause it's being pushed on. How would you seal this off and pit a hose to it?

Also, he needs a mag. How much would one of those cost, and where would we get one?

I'll ask him to look at the threads on the tank, I don't remember then being damaged, just too big, and the in-between peice too small.

mags are about 50 each. I can special order them, or you can order them from a few other sourced I'd be happy to list.


As for the bypass, you either get a tap and die kit and tap in threads where that piece pushes in, then thread a 6mm push to connect into it, or you can jb weld in a barb or push to connect like I did. Either way it works great and gets rid of that crappy tank from the grip. Only downside is you cant run green any more unless you block the hose off and just use the tank in the stock.

I'll ask him what he wants to do about this. I'll ask him to check the threads tommrow. He doesn't have much for the gun and has considered selling it. I co vinced him to keep it and maybe I'll buy it off him when I have the money.

We're both kinda broke so he may not buy a mag right away. But I'll ask for him when he's ready. The current one works, but is missing a small peice and takes a lot of force to get in. Also I told him the cost of an external rig and he really doesn't want to spend that much cash. Hopefully we can fix this and I'll buy it off him and get a rig at the same time.

BTW, when he does sell it, how much should he sell it for? I dot want him to rip me
off cause he has no idea what it's worth.

Originally Posted by G36fanatic...

BTW, when he does sell it, how much should he sell it for? I dot want him to rip me
off cause he has no idea what it's worth.

get some pics of the gun. Also what upgrades are done to it.

Completely stock, plastic body, full H&K trades.

by passing the grip tank is a simple mod, here's some pics to guide you.








The Jac MP5 engine, with Frontline internal. max pressure input is around 140psi.

It looks as though you just machined in some threads, and added the adapter to the hose? I do not have the tools or the skill to do this. For now, I'm focused on getting the little peice to fix the tank. In the future, I would love to have Echihn or someone who knows what there doing work on it.

BTW, Echihn, how much would you charge in labor and parts to bypass the tank?