They don't do no damage, just have to actually hit the internal object to kill it. They do allot of damage but only to things they pass through with limited spall as well which is how they performed historically.
I was able to take out armor with the valentine after I switched them to 0 explosive. Also if you add explosives in you lose the ability to shoot through targets at other targets.
Also for fun:
The 4000kg shell KV-2
Well that was to be expected
Kept going for about 600m
Hit a Pz4 with it, don't know where it went but it's not on the tac map anymore