Display MoreCoulombs law can of course can be verified at macroscopic distances
https://www.pasco.com/resources/video/Pn64KOEpbzs
but at femto distance it is beyond easy measurement..
QCD only has indirect measurements based on models..gluons quarks strangeness..
and high energy collisions.
the latest computations show a mass radius that is only 0.52 femtometers
a significantly less result than the 'charge radius' at 0.8+
Explanation..??
Its very difficult to make any conclusion based on QCD
but for sure at Femto distances
no one can be sure that Coulomb's Law holds
QCD cannot even model the proton magnetic moment after how many decades??
except using dubious extrapolation computation down from the 600 Mevs energy level..
although the derivation is straightforward using the ring current model..
https://arxiv.org/pdf/2207.05212
.
I avoided mentioning QCD for the reason that smashing particles together might just create emergent emissions of energy cascades which have no real practical relevance in the nature of our reality. Changing the medium and the observer for which these particle accelerators changes there outcome, so I'm not really sure we can say these quarks are fundamental or just a byproduct of colliding fields.
I have no explanation of the new predicted mass radius as that is not my wheelhouse.
Most of these theoretical frameworks are our best formalized predictions and shouldn't be taken as scientific fact in my opinion. So take that for whatever it is worth on this Forum 
