The last time I tried the AMX-30 (GDI vehicle, bottom-left square of the first vehicle menu) I presumed its damage was so low as to be useless. I've just done some tests with it again now and discovered something interesting.
It seems that you cannot damage certain armour types if you are <10m away:
amx30_damage_crf23.mp4
Lighter armoured targets (visceroids, many other vehicles) don't seem to be affected by this; they always get hurt even at point blank.
Here's another example where I'm shooting a map tile:
amx30 tiles crf=23.mp4
I've done these tests across a combination of online and offline. Now I'm going to hunt and see if other vehicles are the same
IRL explanation: some shells have a 'safety feature' that avoids detonating the warhead until it has travelled a certain distance/time.
W3D engine explanation: I don't know of any way to do this with LE presets + armour.ini. I just might not have ever considered some relevant numeric field, or maybe there's some clever in-flight bullet substitution going on via scripts. IDK.