Blowing at bucking lips, not making sufficient seal etc...
Could be poor or incorrect/incompatible nozzle/hop
Tight nozzle shoulder or tilted gearbox that causes to rub/restrict return
Tappet not fully returning to seal 101% either needs sanding at front or catching on sector's axle
Plus...
Usual hop unit shifting forward when mag inserted causing hop/nozzle poor seal
(tape in magwell & ensure spring on hop pushing it backwards etc...)
Do the three hand test of hop /barrel removed manually fitted against gearbox
with BB & chrono - will take a few attempts no doubt but FPS goes up when treating
If so then poor alignment/compatibility etc...
Sounds like it just doesn't quite seal against lips, lightly nozzle so lightly kisses the bucking lips so when fires any extra power just blows at the seal and there is your FPS loss
I say it sounds like blowing at lips assuming spring(s) are correct
But either hop shifting, poor compatibility of nozzle/hop or nozzle length, restriction on nozzle movement/final return position, poor alignment if gearbox tilted or out of whack when all assembled - nozzle rubbing as it slides in/out of hop blah blah blah...
The only way is diagnose each individual component and how it operates
Or
Go back to stock parts & retest, then carefully check/measure/compare each component you replace with other parts seeing how efficiently they operate
The moment you start changing and replacing stuff without double/triple checking EVERYTHING, then you leave yourself wide open for headaches if not serious migraines
Rebuilding a box from scratch is involved even more checking from scratch on every component as you can't quite compare stuff like stock nozzle lengths, if after market selector plate works 101% or exact same as stock one, if a replacement cut off lever fully resets on the trigger trolley, if the wanky flat speed trigger jumps off the trigger trolley at full pull etc....
(Fuck me there can be LOADS & LOADS of compatibility issues changing shit over)
Hence it is easier to change just a very few stock components only when really needed and paying very very very close attention to detail comparing length of nozzles and full efficiency of the replacement parts you fit
Even then, after all this you still get issues in the assembly if stuff shifts like tightening gearbox/stock tube that tilts gearbox up at front or hop unit tries to shift forward when mag is inserted etc....
What nozzle did you fit - if SHS the single o-ring is better imho as the nozzle front completely rounded without the tiny nicks to prevent possible BB suck on the double o-ring nozzle
Nozzle lengths vary, M4 is "usually" around 21.45mm but other makes/models use shorter ones, uses a SHS M4 nozzle in say an ICS split M4 gearbox ICS rotary hop and you will have feed issues coz ICS M4 nozzle used is shorter
All this TM compatible BS is at best compatible -ish and shit always needs to be checked very very thoroughly unless you have a good supply of paracetamol or if you can't won't check shit then only replace parts with genuine components from your gun's manufacturer type of thing
(even then poor batches or poor assembly can occur)
Nozzle not sealing on bucking lips is my guess but could any number of reasons or a culmination of factors causing issues
Which is down to you or somebody to go through & methodically test/check stuff blah x 3
More info and pics might help too, if you have a bearing spring guide or not, bearing spacer in piston - all of which adds more spring compression/power or lowers if removed
Correcting AoE lowers FPS by say 15fps but is usually replenished if installing a bearing spring guide
Spacer or bearings inside piston can be like compressing spring a further 2 or 3 teeth, so can vary by another 30-40fps etc...
Plus different gun's/barrels mean a m100 spring could shoot 300fps to say 360fps in another on full piston stroke - let alone volume or short stroking
Negative is the best, been watching his vids since he started. I use very small amount of halfords spray silicone grease. The thing that I find most odd is the consistency of the fps. If there was air leaks etc I would be seeing a wide variance in fps( I assume)
If the lips are blowing then anything past 320 is expelled by pissing at lips
Sounds weird but does happen in some cases, almost what you push out the lips start to blow at that xxx figure coz the seal is poor and at that point excess power blows the seal
But yeah send it off to Luke might save you a lot of agro (and my fingers)
