ICS M4a1 issues, +falling piece needs indentify

[Jackalex36]

Hello!
I bought a ICS M4a1 retractable stock a few months ago, and I'm having some issues with it at the moment. It's still stock settings by the way.
Basicly, the gear make some REALY weird sound, it's like spinning in the empty or whatever... nothing similar to the usual firing sound..
I opened it up and I noticed that the first teeth on the plastic-cheap piston was stripped, and I think this is the main cause of the failure to engage the whole process.
Also, when the two are connected, I noticed that the piston isn't moving back and forth. So I think this is the problem right? Can it be something else?

If this would be the problem, then I would like to know if I should buy another piston. A polycarbonate one or an aluminium one? (both ICS). I don't want to change anything else, and I heard the weight or whatever changes something..? I want it to be durable :S.

Also, right before this problem happens (coincidence?), a small metal cylinder fell off the gun. I don't really know if it was from the tip of the nozzle or from the mag (since there was no mag in when that happened)... but what is that part for!!??? I can't figure out where it's supposed to go on the exploded view... here is a picture:

I think it's supposed to go at the tip, like between the inner barrel and outer barrel, to avoid some vibration or something, but it doesn't seem to stay in place.. :S?

Thanks for the informations!!!
PS: Sorry if it's confusing, i'm native french and it's sorta hard to explain those things in english

[Kos-Mos]

your piston is stripped.

Happens all the time with clear ICS.

Buy a TM stock piston and install that instead. You won't have problems for the next 50 000 rounds.

That brass sleeve does go at the tip of the outer barrel, between the inner and outer. It is not necessary, but you might want to re-install it anyways.

If you bought the rifle off Vlad's, send me a PM. I should have a piston in stock to fix it.