If you wanted to experiment you could take a pair or wire snips and cut off one ring of spring coils at a time until you got to the velocity you want.
also more info here on Laylax (First Factory) springs:
First up, spring rating and FPS (Courtesy of Airsoft Dynamics):
* 110SP - Approximately 110m/s with 0.2g BB.(361 fps)
* 120SP - Approximately 120m/s with 0.2g BB.(393 fps)
* 130SP - Approximately 130m/s with 0.2g BB.(426 fps)
* 150SP - Approximately 150m/s with 0.2g BB.(492 fps)
http://www.airsoftcommunity.co.uk/fo...howtopic=45492