u/AddictedToComedy — reddlx

Quick notes:

M16 Technical Data Package is available here. For the action spring, see drawing 8448629 on page 36.
M4A1 Technical Data Package is available here. For the action spring, see drawing 9390022 on page 157.
Outside of the TDP numbers, all of my spring data is captured using my spring testing rig.
All springs in my charts/tables were new when tested.
My charts and tables are meant to report objective measurements: not pass judgment. I'm not saying that Spring XYZ is "bad" because it's outside of the mil-spec range.
F1 = force exerted by the action spring against the closed bolt
F2 = force exerted by the action spring against the fully rearward bolt

See comments for more detail