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Full case study, m120 no fps gains.

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I ran into the issue with AUG, full write up below.


I own a ASG AUG A2, current setup:

Shs m120, doube oring cylinder head, shaven tappet plate, metal nozzle with oring, metal hop-up (shimmed towards mech box), teflon on the bucking and, mad-bull 6.03 (509mm) = 330-338fps


Previous spring operated when new at 345fps after 8 month gone down to 280.


After instalation of M120 (longer than original, so no mistake here), guide and piston (aluminium) the fps did not achived expected 360-380fps. The original spring had a weight attached to the front of it, and the spring guide kept the back end of spring further away from the rear of mech box (pre-compression?).


The New spring is not compatible with weight hence the heavier piston.


I belive that system is not very leaky as fps is is rather consistent with odd anomaly +/- 10fps (hop-up: off) The mech box is shimmed and secured so sits snuggly with almost no play, hand compression test with the nozzle shows no leaks. When testes with piece of paper on the mag well bb feed, the piece of paper just moves to the side (not flying away).


So far I came up with couple of ideas:


-Air nozzle to short (0.5mm or something along this lines)

-Lonex bucking not sealing under pressure(too soft?)

-too light piston?

-Too weak spring?

-wrong cylinder volume (v3/4 I think) for this length of barell ( measurements to be perforemd over weekend). The cyliner is inserted with the notch on gearbox in right place.


Could some point me in the right direction? Did I missed something obvious?


Thank you for taking the time to read this.

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Agreed, you definitely have the wrong cylinder.


Also try swapping out the piston for a lighter one. A lighter piston will accelerate faster, causing a higher pressure spike and higher velocity. .20g are on the light end of the bb weight spectrum so you would want a lighter piston. A heavier piston may help with energy output when using heavier bbs.

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One more thing, AUG's don't hold the gearbox very securely in place, and this obviously tends to make them more inconsistent. Have you done any mods to tighten down the gearbox? A common mod is the "bolt mod", I did a different mod to my AUG with a smaller screw in top of the gearbox. You have to remove the fake bolt cover do this though.

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Cylinder changed to type 0: avg. 437fps achived.


Shortened the SHS m120 by 2,5 coils resulting 401fps (I hope that the spring will loos the power over the time)


-Lefse: I have alter the "mech box locking mechanism", from the back I have a bolt that pushes the mech box forward mounted in the plastic retainer.


Thank you again for the input.

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