I recall that the ACOG when used on M4s and M16s is typically zeroed for 100m at the tip of the chevron, and then the scope provides range markers when hold over is required. It does state in the manual that you can do a quick zeroing of the sight for 25m by using the red tip of the line below (kind of inside of) the chevron but that you should take the opportunity to zero it properly at 100m when you can. No idea about the M16 irons, though.

I haven't found the 75m zeroing to be problematic for BAs. The only rifles that seem to have trouble with this are rifles with lower velocity such as the G95 when shooting at like 105-115m. But that's not due to the 75m zeroing. That's due to the bullet from that rifle having more drop. G98 handles that shit like a champ, and I've found that the 150m zero isn't really even necessary on that rifle since the holdover for a target at 150m when zeroed to 75m is quite small.

If you really want to learn an appreciation for zeroing, take the Martini Sniper for a spin. "Nothing shows bullet drop quite like a Martini Snipe."

I remember playing the BAs for a long consecutive time before the zeroing change hit BF4.... From one day to another it became so much easier.

Yeah, BF1 is a different story, but if you have played with the difference yo could have felt the improvement from zeroing