Balrog wrote:Sorta confused on when exactly it pays to switch from using AP to HE, open-topped vehicles make some sense and I've had some success with it but it seems to be a crapshoot other times.
It very often doesn't. You can use HE to reset the cap counter because even a couple of points of damage to an enemy's tracks will take off their cap points, but it's super unreliable against anything that isn't complete tinfoil.
I don't tend to carry any.
To expand on my previous point now that I have a proper keyboard at my disposal...
HE, unlike AP, is usually effective almost in direct proportion to gun calibre. Bigger shell = more high explosives = more boom. More damage lets the HE shell 'burn' through armour and deal damage even on a non-penetrating hit.
If you have a tank with a big, particularly big-for-tier gun - like the Soviet 122mm and 130mm guns - their HE will reliably ruin the day of an artillery or lightly-armoured light while a titchy British 84mm gun a la Caernarvon or Centurion will have much lower HE:AP damage ratio, so you might as well fire AP and reliably deal damage.
HE also has no normalization (ability to penetrate angled armour) or overmatching (ability to penetrate extremely-angled but very thin armour). I usually carry a handful (say, 3-5 rounds) on all my vehicles in case (a) I see an artillery or (b) I need to reset a cap as Vendetta said.
Overall, I carry about 85% AP/10% Gold (APCR/HEAT)/5% HE on most of my tanks.
If you want the detailed math on the different ammunition types, http://wiki.wargaming.net/en/Ammo