Hectic, you've got smoking-gun evidence of PE, so don't let yourself get distracted by the discussion around weak pistons and AoE. You need a strong piston, you need to correct AoE, but the reason your orange piston failed was because you've had PE (pre-engagement).
The reason for PE in your case could be anything, but it can be caused by too weak of a spring, a heavy piston, or a piston that had trouble moving along the rails. You might have also had a BB jam in your hopup chamber and you kept firing full auto (if your gun was a little off its rocker, this could have easily happened).
All of those things can cause PE. In your next refresh of this build, solve AoE, get a strong piston, but make sure you've prevented pre-engagement. If you put in a slightly stronger spring but steal away volume using a sorbo pad (which you'll need for AoE anyway), you can neatly tie up both of these problems with a single solution.
+1 on the lonex red pistons.
Don't forget to check that yours moves up and down the gearbox nice and easy!.
Also Hectic, Stealth, let's all chat about this at Finch's on Sunday
