[38Super]

Hi All
I've just put my SRS together over the weekend and I would appreciate people's thoughts on the compression I'm getting.

This is what I get with my finger over the muzzle (muzzle cap removed). I can clearly hear air escaping from the back of the cylinder. I tried just silicone oil on the piston cup and greasing the cylinder. I've cleaned it out and re-lubed a couple of times just in case with no difference. I'm getting 331 +/- 9 fps which is less consistent than I would like.
It is the same if I take the bolt out and put my finger directly over the nozzle.
Should I be able to hear air coming from the back of the cylinder?

I'm not sure what the piston cup is supposed to look like so I'm not sure if the shape of mine is normal.
I've ordered a new piston cup anyway just so I can compare.

Any thoughts, comments or ideas are appreciated.
TIA

 

[SiliconeSword]

Most likely the piston cup, definitely try the one you bought

 

[38Super]

Most likely the piston cup, definitely try the one you bought

Should arrive in a few days. Fingers crossed.

 

[38Super]

Update.

Fitted the new piston cup to the SRS and it's made a big difference.

Before:
331 +/- 9 fps
Finger over the muzzle test - 9 seconds for the piston to stop moving
Audible air leak from back of cylinder

After:
337 +/- 3 fps with around 1 shot in 10 dropping to 331 fps.
Finger over the muzzle test - 40 seconds plus
No audible sound of air leaking.

Definitely suggests a faulty original piston cup.