Probs I have with any type of 'ammo counter' or 'traffic light system' is that someone will check out the codes and values and then will know exactly how many rounds are left inside. What about smaller mags for the pistols or the RC.50?? If you divide the available amount into three 'groups' you end up very very close to the actual number. So the traffic light system would end up to be very precise and then you can setup a full ammo counter then too cause it would only look like a shiatty feature then.
Randomness would only stirr up trouble cause even for medium mag sizes it can give you a false impression and can switch from 'yellow' to 'red' easily... and forget randomness for the pistol mags fully... the only difference you would get would be one or two rounds or empty and full.
In addition ... maybe you guys never noticed but ammo you pick up, gives you the EXACT amount of rounds left within presented on your HUD... maybe watch it a bit closer.
So, the only 'problem' is that a weapon you pick up does not 'tell' you how many rounds are left within the mag or if a 40mm is loaded or not.
Well, one way would be to pickup another mag or weapon of the same type to get another magazine to reload and then drop the second mag to pick it back up again to get the amount of this one then. The other one has to have more or the same amount of rounds left within cause the soldier automagically grabs the fullest mag on reload every time. Sure, not a perfect method, but one that works if you have another mag available. The time needed for this comes close to actually counting the rounds within I guess.
For the case you have no spare mag somewhere... well... the world isn't perfect
So no need to add any type of ammo counter into INF in my opinion.
Beppo