I use this spring: 9637K26 (McMaster part #).
Its a beast. Its more powerful than the AR-15 spring. You get 5 for $10. Each spring is 11" long.
YOu were not kidding that it's a beast! ! You said you used this in a Long Shot? I"m modifying a Recon CS-6 and i'm making some of my own "new" modfications to it, but taking the idea from DeceitfulSteve who used an AR-15 Spring for his mod of the Recon CS-6 (see: Adding Another Spring To The Recon, And a reason to use the stock)
I'm wondering if now I should use the AR-15 Spring (need to buy one if so) instead of the one quoted above. I'm concerned because I need to compress it by 5.5" instad of the original 3.25" as it is now. I'm expanding the air resevior and so the orange piece (what I call the Breach Block) will slide back 5.5" instead of the 3.25", so the spring needs to expand by 5.5". The 11" spring is plenty long, but will it compress enough without breaking any plastic pieces