Very irregular FPS on AUG questions

[Jimski]

Hey folks!

I'm upgrading a CA AUG A1 and I'm getting a really irregular FPS, with 3 main readings, at 287, 310/315 and 330/340 fps.
The gun seems to 'zone' in either of these speeds for a few shots then change.
I noticed that when I slap the gun between shots, FPS changes.

since the CA internals are pretty good, I just threw in a spring (MS100SP ).
I had to heat up the piston head's O-ring to get a better seal.

I have tested the nozzle, hop-up unit, hop-up sleeve and barrel extensively and switched them with other upgrade parts; whatever the combinations are, I still get this inconsistent FPS.

-The cylinder head is teflon-taped where it meets the cylinder
-the hop-up unit's front is sealed with wrap
-sleeve is new,have tried others, same result
-right now it's a TM cylinder head+nozzle going in a CA stock hopup, result was the same with CA head+nozzle, in either TM stock, CA stock or CA upgrade hopup, with any sleeve, any nozzle I have and any barrel.



here are my possible conclusions:
-heated O-ring is inconsistent?
-spring is inconsistent
-air leak hidden somewhere but where?
is it possible that a perfectly sealed system un-seals at the moment of impact of the piston? where would that be?

what do you guys think ?

thanks !

[kalnaren]

I'd guess the O-ring. Any other airleaks should be more or less consistent.

[Jimski]

ah, good point, thx.

[Sha Do]

Originally Posted by Jimski

Hey folks!
here are my possible conclusions:
-heated O-ring is inconsistent?
-spring is inconsistent
-air leak hidden somewhere but where?
is it possible that a perfectly sealed system un-seals at the moment of impact of the piston? where would that be?

what do you guys think ?

thanks !

I'd start off by switching out that piston "O"-ring with a slightly larger one.
Also, check how well your hop up/mech box is meshing as this could also result in a potential air leak robbing you of FPS. Try a couple of shots with the mag butted onto the ground, then a couple gently pulling down on the mag. If there is any consistant differences in the FPS, then you definitly have an air leak in the hop up area. To solve this you'd have to shim your hop up back towards the mech box with some "O"-rings over the barrel and infront of the hop up unit, BUT, make sure that there isn't an debris inside the receiver that is preventing the mech box from resting all the way forward.

SHA DO

[Jimski]

very good advice, I'll try, thx!

[IRONSIGHT]

Also check that the plate that hold the mechbox in from the rear is screwed in properly. If it's not, the action of you pulling the trigger will actually push the mechbox back, away from the hop unit causing a gap. You might be able to see if the mechbox is moving back by looking thought the ejection port while pulling the trigger. Do this with no battery in the gun as the movement might be hard to see with the mechbox cycling.