If you ask me an M110 spring is enough (~360-380 FPS), no need for an M120 to try and reach the limit, remember limit not a goal but you seem reasonable enough to understand that.
Also yes a paintball chrono will work, as will a real steel one (that is if you have access to a gun range or know someone with a real steel chrono). All it does is measure the speed of the projectile being shot through it, hell you could use a paintball chrono to measure how fast you can throw a pen or rock through it if you were so inclined to do that.
ಠ_ಠLess QQ more Pew Pew
READY TO >> RACE