[1tonne]

This is a list that I put together for SP ratings if it helps:
SP130 = 445fps
SP140 = 480fps
SP150 = 510fps
SP160 = 545fps
SP170 = 581fps
SP180 = 615fps
SP190 = 650fps

You are most likely best to get a SP160 (if you can find one) and cut it down. The SP150 will do 510fps or there about but it will lose it's rigidity over a couple of months. Higher FPS springs often have thicker wire and so they last longer. Also since you would have to cut it down it would not be compressed as most springs are when in the cylinder and so it will last even longer.

Also VSR10 Laylax springs will fit in a Maruzen/WELL L96

 

[1tonne]

Yikes. It is an old thread. I never noticed that.
Anyway, I have been in the process of making a thread regarding springs: http://www.airsoftsniperforum.com/3...sing-right-spring-making-work.html#post127126
It has some info on there that a lot of people would not have thought of.