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New Build Possible PME - please help

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Hi I am looking for a bit of advice after running into trouble on my first build, basically after only about 100 rounds my piston broke on full auto, when I took it apart the first metal gear closest to the piston head had snapped off along with the front of the piston. I have been reading lots of forums but still unsure if I have PME or some other issue as all the other teeth on the gears and piston look ok and if I did have PME I thought it would be the other end of the piston which would suffer. Or have I just been unlucky and had a bad piston which broke up ?

  • Gun is a G36C
  • Piston was a Guarder Piston and Head with only one metal tooth
  • SHS 13:1 gears – shimmed with selector chip installed
  • High torque Motor
  • Rewired with 16g wire
  • ABB Mosfet
  • SP110 spring
  • On 7.4V Lipo

ROF when I tested was around 33rps


I am not to worried about the ROF but would like it up around 25 and need to keep the FPS below 350.

I would also like to try and avoid short stroking if possible (just do not want to go their).

Any ideas why the piston broke up or was this just a dud? and what I need to do to avoid this happening again? should I go back to 18:1 or 16:1 gears or would this still give me a PME issue with this set up


Sorry for all the questions

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I doubt it was caused by PME, or it would be the pickup tooth and the teeth closest to it that would be broken. I'm guessing that you simply overloaded the piston. You're running an M120 spring at 33 RPS, that's a relatively high stress setup and will require a very durable piston like an SHS or CYMA metal teeth piston or a System Supercore.

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