Fps issues with an ICS L86A2 LSW
 

I bought an ICS L86A2 LSW last spring and its fps is low. No matter what I do, springs, pistons etc, I can't get the fps to higher than 370-380. Does anybody have a similiar problem abd /or what the problem is and how to fix it.
Thanks for your time.

of course you realize that gun has a 3 position spring guide right?

Spring guide
 

Absolutely I'm aware of that, it was a selling point for me. Like I said, I've tried everything common sense and experience has taught me. My buddy, who is a wunderkind with the guns is stumped too. This is my last hope before I cave in and I pay a professional to take a look at it.

Perhaps a hop up sealing issue with your gb?
Hop up rubber is fine I'm assuming?
No cracks in the nozzle, does the nozzle have an o-ring?
Is the pistonhead okay and sealing inside of the cylinder properly?
You said your friend is good with guns, I'm assuming you guys tested these things for airseal but it's my 2c