Losing 40fps

[perky416]

Hi guys,

I have a umarex G36C, i beleive its made by ares. For as long as i can remember with .25's its always shot at around 300fps (330fps with .20's). Last week it chronod at 290fps, last night at 280 and today at 260 fps (290 with 0.20's). I believe the spring was a guarder SP100 that i fitted a couple of years ago. I have a quick change spring so i fitted an M120 (usually around 400fps) however it came out at around 360 - 370 fps.

Something other than the spring seems to be affecting my FPS, its around 40 lower than what it should be. I cant access the pison to check compression as the gearbox screws seem to be welded in place (i snapped one trying to gently open the box). I cant change the nozzle as it seem I have to take the gearbox appart to do it.

Does anybody have any ideas as to what else can be affecting my FPS? I have no hop when testing and a 6.03 prommy barrel.

Many Thanks

[Spatch69]

Re: Losing 40fps

Airseal, air seal, air seal....

Hop rubber, how old is it?
How long since gearbox was serviced?
Piston o ring is probably shot, gearbox dry etc

[dapprman]

Re: Losing 40fps

One other thing - probably silly, but do you clean your barrel regularly ?

[perky416]

Re: Losing 40fps

hop up rubber is the stock one, but it is in really poor condition, i have a new one on order should get here later in the week so i will try that.

gearbox has never been serviced as I cant get into it without breaking the screws. After my next game this saturday i am going to open it up regardless of the screws.

barrel is cleaned after every game as its a TB.

Thanks

[RitchieTheBrit]

Re: Losing 40fps

You will need to crack that sucker open and check the o-ring and nozzle, work forward through the system.

1. Take the spring, tappet plate and air nozzle out, press your thumb firmly over the cyclinder head and try pushing your piston into the cyclinder. You should notice an increase in pressure once the cyclinder head passes the port. If not, inspect the o-ring. If you can't press it all the way in with your thumb in place, then all is good.
2. Fit the tappet plate and air nozzle, repeat the same test. If you lose pressure, inspect/replace your air nozzle (prefereably with an o-ring version).
3. Rebuild your GB, making sure you lubricate and shim (probably a good time to correct AoE if you haven't).
4. Rebuild the rifle, chrono. If you're still down from what you expect, then your airseal between the air-nozzle and bucking is suspect. Check and replace.