What is the problem?

[B.O.P. Hawk]

Before any upgrades, I had a G36 with a low rate of fire that shot 340fps, and could not hit a person at 50ft.
I now have a G36 that shoots rather quickly and at 209fps, that can hit a quarter at 100ft.

As you can probably tell, I have an fps problem.

Everything went well until I installed the piston...
I wanted a G36 DMR, so I bought a TBB, a new bucking, and a stronger spring. My gearbox could not pull back the M130 spring, so I bought a high torque motor, and then a higher voltage battery. It pulled the spring back, but after four shots, I heard a loud crack-smack from inside the gun; I had broken the piston.
I put the old spring in and a new piston. That's when my fps dropped.


I suspect that the o-ring is the wrong size, but I cannot find my old one.

I did a compression test under water. It went in ever so slowly, and bubbles came from inside the cylinder.. from between the cylinder and the piston, which only partially proves my hypothesis.


Can anyone tell me what the problem is, and/or what I can do about it?

[dos_Santos]

I have never heard of the water immersion method, but I test compression by simply ramming the piston in the cylinder while blocking the nozzle. That will give you a pretty good indication if you have compression issues.
Did you properly grease the o-ring? Is the cylinder installed in the right direction?

[B.O.P. Hawk]

Everything is installed properly. There is grease on the o-ring, but not very much. What is the best way to insure that is done correctly?

I did the regular compression test, the one you do, but I did it underwater to determine where the leak was (Air nozzle, cylinder head, piston head, o-ring, etc...).

[Nec]

Try replacing the O-ring with a #14 O-ring, available at your nearest friendlily neighborhood hardware store.

[Merchant]

Oooooo! I love this game of guess the problem!

You want perfect compression in the gear box between the cylinder, piston, and cylinder head. These are the 3 easiest spots to get a good seal. Once you know you have a perfect seal between these then put on the air nozzle on and see if it is leaking there. if it isn't, then your leak is between your new bucking and the barrel, hop up chamber, or nozzle.