Compression problem

[cripto]

When I chronoed my gun about 4 months ago I was shooting 400 fps with .20. Yesterday at Phantom Hawk it chronoed 286 with .25. I opened up the GB and everything looked fine,noting cracked or anything. I just installed a new bucking and I've heard of a break in period. Could the new bucking be causing the problem? Thanks

[Jeremy314]

Could also do with the piston O-ring not engaging enough for a good seal inside the cylinder take out the whole cylinder assembly, pull out the piston, and put your finger over of the air nozzle put the piston at the opening and let gravity push the piston as far as it can. If it slides easily all the way down, then you need to stretch the O-ring a bit.

Easy way to do that is to take the O-ring off the piston, and stretch it over the outside of the cylinder, put some 100% silicone oil (not spray silicone of any sort!) on it then use a lighter to heat up the O-ring and it will soak in some of the silicone and expand.

I did this when I was putting an M100 into my KWA G36 with a 6.03mm TBB, which was shooting 330's with .25s and an KWA120 spring. After wards it was shooting 330 with .25s and the M100.

[cripto]

Thanks for the advice! Where can I buy 100% silicon oil?

[Jeremy314]

you can go to an RC hobby shop and ask for shock oil, it's usually 30 weight if I remember correctly and it doesn't have any of the additives that cause spray silicone to eat O-rings and other seals.

[Smoke]

Check to see if your bucking and air nozzle are getting a good seal.I have changed buckings and gotten a bad seal before  I would  do as Jeremy said and check the  o ring first and then start moving  on towards the end of the aeg checking everything else from there....let us know your progress

[idiot88]

Any chance it might be the chrono itself?  Did you use the crono with two antennas?  Did anyone else get lower chronos than usual yesterday?  Mine was about 30 fps lower yesterday than it was a month ago and so was someone else's.

[cripto]

yeah thats the chrono I used. My cylinder is ported and the gun is an m16. should I get a solid cylinder?

[SteevoLS]

I tested a few of my personal guns, and they all chrono'd accurately based on the last time I had chrono'd them. Even if he was just chrono'd low, he's still shooting lower than he should be.

[Dominum]

The long and short of it is, open it up and check all the compression. There's a ton of things it could be, but speculating won't fix or confirm any of them unfortunately. You can find 100% silicon lube on many airsoft retailer sites, like AA.

[cripto]

Well I think it is fixed. I got a new O-ring at Ace(The old one wasn't worth saving) and the fps appears to be back to normal. Thanks for all the help guys! If only I had a chrono...