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Not seeing the typical signs of PME (chewed up pickup/rack). Did you see the same issue with a lower powered battery (7.4v instead of 11.1v)? What spring are you using?
 

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M105 with a 4t SS, could see PME being possible. Maybe try using Perun ROF control and seeing if there's any difference as you slow the cycle down? Make sure AB is on, no pre-cocking.
 

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Potentially, although 5t SS could start messing with your timing - may want to take one off the release side instead. What's the current FPS (before it started acting up)?

Personally, I'd start by using ROF control and/or a 7.4v to ~confirm if it's PME. If it looks like it is, you may be able to get away with just lightening your piston assembly some more - every g you remove gives you more headroom and you might be right on the edge if it cycled ok previously. Get that piston assembly under 20g one way or another lol. If that doesn't do it then I'd try adding a spacer to the spring guide to give it a bit more oomph if you can gain a few fps while remaining legal - if not, stepping the spring and taking another tooth off may be needed. Or be lazy and just use ROF control to keep everything in one piece - definitely done than a few times.
 

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Must be quiet a barrel to squeeze 340 out of a m105 with a 4t SS, if you can get it to cycle smoothly that'll be one heck of an efficient setup.

Removing the bearing from the piston head will decrease spring compression by ~5mm, will lower fps slightly. Just a heads up. I found some hard plastic washers of approx the same size, 0.5g vs ~5g bearings.
 

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Will have to listen to the vid somewhere quieter than here lol

I check for PME with a Chrono or by watching the amps the motor is using - will spike at the end of a cycle if the piston catches.

Buffers, sorbo, etc - prob ok here but can be dangerous in high speed guns. The buffer compresses, that's it's job, but in doing so the AOE becomes inconsistent which causes a lot of stress/wear on pickup/gearset/bearings, FPS creeps/wanders, and if you're unlucky the buffer separates from the CH and gives you some nasty PME by jamming your compression set. Better to have a light spacer behind the piston head for speed - can't compress, can't come loose, stable, etc. Does add weight to the piston assembly, but only half a gram or so if you make it out of POM ABS etc. All imo / based on my experience oc.
 

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Not seeing drops on 7.4v narrows it down, PME is a strong contender but usually it's more consistent in auto than you're seeing... Might be because its marginal? Piston rack will tell the tale.

How's your nozzle look/feel btw? Got good spring tension, feel smooth, no/little wobble, centering OK, etc?
 
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