TM G3 SAS low fps problem

[TJchoosespikachu!]

i've upgraded just about the entire upper gearbox of my TM G3 SAS and it seems like the fps is still way lower than it should be. i'm using a guarder sp 90 which is supposed to be firing somewhere around 335fps according to http://www.poweredgehawaii.com/SpringTest.asp but it's still cronoing at 280. i've installed the same spring in a couple of friends' guns (mc 51, m4a1) and they all seem to be shooting in the 330 range. here's a list of what i have installed:

area 1k spring guide with bearings
guarder sp 90
systema aluminum piston
systema silent piston head
systema silent cylinder head
systema nb cylinder
systema g3 nozzle
area 1k tappet plate
systema shims
area 1k bushings

think my SAS was shooting in the 280's bone stock when i first got it... it's frustrating that it's still shooting around the same fps after all these upgrades. i've checked cylinder compression and it seems to be leak-free. i thought it might be the air nozzle but a brand new systema one didn't seem to help. what could the problem be? i'm about to go crazy!!!

[Skruface]

Lol. Do you have a cylinder with a hole in it? Make sure the hole is at the BACK.

[Tankdude]

Is the hop up turned on.

[TJchoosespikachu!]

yup holes in the cylinder are at the back and hopup is on. it makes no sense!!!

[Avenging Angel]

Sounds to me like the piston head isn't sealing properly with the piston chamber. Disassemble the gun and make sure that it's forming a complete proper seal.

[TJchoosespikachu!]

yeah compression is perfect... no leaking whatsoever. this has me totally stumped. i think i've replaced every part that would effect fps inside of the gearbox. the only thing i haven't touched is the hopup chamber and the inner barrel. could it be possible my hopup chamber is wacked and is leaking air? i don't know what could be wrong!!!

[mcguyver]

how are you testing compression? are you just pushing in on the piston while holding your finger over the nozzle? this will wok in slow speed but in normal (high speed) opeartion the piston head o-ring may not be moving front-to-back in it's seat to allow for alternating vacuum/compression cycles. make sure to use a silicone grease with about a 40 weight or so (tough to gauge exactly but basically it's much thinner than standard grease but thicker than the silicone oil used for gbb lubrication).put some on the oring and inside the cylinder until both are well lubricated but not overly juicy (sorry for the simple, seemingly unscientific, terminology). re-assemble evrything and try it out. i used to have a similar problem with some types of cylinder heads using to heavy of a cylinder grease (especially the gaurder "explosive piston heads"). if the graese is to thick it "gums up" that piston head o-ring, not allowing it's front-to-back movement and resulting in reduced compression.

btw in your friend's m4, it uses a full capacity cylinder and that extra air volume will increase the output of the gun. your normal capacity (some say "reduced capacity") cylinder is not capable of big fps without a cylinder change.

[Mantelope]

Mislabelled spring? Remember the bushings on the piston head?

[yanhchan]

maybe your barrel is dirty?

[TH_JJ]

I think it is your spring...
A friend of mine has the same type of spring installed in his M15..
His compression is near perfect, so I assume the spring is the problem..

Prometheus makes better springs..