Which Spring?

[Kunithrayin]

I have the Shocktech spring kit from sundragonpps.com (Heavy, Heavy/med, Medium, Light)
First which one should I use with my stock internals, 16" barrel MR1?
And Second which with my brothers Stock Pilot ACS?

[bamf-hacker]

Start with the medium spring and then chrono your marker. If you are in the right range or close enough to adjust it with the adjuster knob then you are good. If it is still too high or too low then start switching the springs and repeating the chrono until you get the FPS you are looking for.