Originally Posted by slink182
Is the spring marked as a "100" spring? Otherwise, how are you sure that it's an M100?
Spring codes (100, 110, 120, etc) are expressed in metres/sec. Most folks run M120 springs.
It was specified as an M100 from the distributor. Also, the field where I live is completely outdoors and therefore 350-400 FPS is the desired level.
I might just purchase a System M110 or M120 for outdoor and replace it if I ever get the opportunity to play CQB indoors.