Each different shell type has different uses, different situations where they will excel. Below are some of the shells’ characteristics and what type of armour they are best against.
AP

-AP is generally the best shell for any situation, good shell velocity, high normalization, low shell drop-off, and it can go through objects.
-Usually AP is the standard ammo of most tanks, but many tanks may have it as a premium round.
-Can overmatch? Yes
-Ricochet angle: 70 degrees
-Shell normalization: 5 degrees
-Penetration decrease over distance: Low (generally)
-Detonation on objects/spaced armour? No
–Shell velocity: Average (generally)
Where AP is better than APCR or HEAT:
– Against thick and well angled armour (angle less than 70 degrees)
-Against tracks and spaced armour, and going through objects.
-Against well angled armour at distances (shells may be slower than APCR, but will penetrate more effectively)
APCR

-APCR is usually a premium round, but many tier 8-10 tanks have it as standard ammo.
-APCR is better at penetrating armour when close to its targets, since most APCR rounds lose quite a large amount of penetration over distance.
-Can overmatch? Yes (but much less consistently than AP)
-Ricochet angle: 70 degrees
-Shell normalization: 2 degrees
-Penetration decrease over distance: High (generally)
-Detonation on objects/spaced armour? No
-Can penetrate through spaced armour? Yes
–Shell velocity: High (generally)
Where APCR is better than AP:
-Against fast moving targets at long distance.
-Against non-heavily armoured targets at long distance.
Where APCR is better than HEAT:
-Against spaced armour of any type.
-For shooting through obstacles such as fences or sheds.
-Against long range targets with light armour or fast movement.
HEAT

-HEAT is usually a premium shell, very few tanks have it as a standard round.
-Generally HEAT has the highest penetration in the tier. This is to make up for it having no shell normalization, for this same reason HEAT gets more pen from using Calibrated Shells than AP or APCR.
-While it can penetrate and deal damage through spaced armour, its much less consistent and reliable than AP or APCR, so is generally discouraged for use on spaced armour.
-Can overmatch? No
-Ricochet angle: 85 degrees
-Shell normalization: None
-Penetration decrease over distance: None
-Detonation on objects/spaced armour? Yes
-Can penetrate through spaced armour? Yes
–Shell velocity: Low
Where HEAT is better than AP:
-Thin but very well angled armour (above 70 degrees).
-Very thick armour that’s not well angled (since it has no normalization).
-Very thick and flat armour at long distances (since it won’t lose pen), though if the target is moving its harder to actually hit.
HE

-Most tanks in game have HE as the 3rd shell in the ammo loadout, the only tanks that don’t have it are tanks that have no HE, or have it as the 2nd shell (like St Emil).
-Generally HE has very low penetration, but higher damage than AP, APCR, and HEAT.
-Can overmatch? No
-Ricochet angle: Does not ricochet
-Shell normalization: None
-Penetration decrease over distance: None
-Detonation on objects/spaced armour? Yes
-Can penetrate through spaced armour? No
–Shell velocity: Low
Premium HE

-Only 4 tanks in game have Premium HE, which are the T49, T49 Fearless, BZ-68, & BZ-75.
-The other tanks with Premium “HE” actually use HEP or HESH (explained below why this is not the same as premium HE).
-Generally, premium HE has less penetration than other similar HE type ammo, but does increased alpha damage.
(Example, T49 has 10-15mm less penetration than other 152mm HE shells, but it does an extra 100 damage for its damage level. BZ-75 has 20-30mm less penetration than other premium HE shells, but does 780 damage.)
-Can overmatch? No
-Ricochet angle: Does not ricochet
-Shell normalization: None
-Penetration decrease over distance: None
-Detonation on objects/spaced armour? Yes
Can penetrate through spaced armour? No
–Shell velocity: Low
HEP & HESH

-HEP and HESH are 2 different names for the exact same type of shell. Both in game and in real life they have the same performance and effect on enemy tanks.
-In game, HEP and HESH do not perform differently to standard HE, they just have different penetration numbers. For this reason they are shell names, rather than an actual different shell type. (You can check shell names in the garage, under ammo, then click the shell icon image).
-These shells generally have increased penetration over standard HE, but with the same or less damage.
-These shells are the highest penetration HE-type shells, generally they have over 100mm of penetration, but there are some with less (examples below).
-In game, they can be either a standard ammo, or they can be a premium ammo. The standard ammo type of HEP/HESH is generally called “cheap HESH”.
-Can Overmatch? No
-Ricochet angle: Does not ricochet
-Shell normalization: None
-Penetration decrease over distance: None
-Detonation on objects/spaced armour? Yes
Can penetrate through spaced armour? No
–Shell velocity: Low
Examples of HESH & HEP:
Pen is only 0-10mm above average, shell name is HESH or HEP:
HESH: Chimera, FV4005, FV217 Badger, Progetto 65.
HEP: Kunze Panzer, Leopard PTA, Leopard 1, 121B, M48, M60.
Cheap HESH, where pen is 25-60mm above average:
HESH: Tortoise, Chieftain Mk.6, Conqueror, FV215b, Vickers Light, Standard B, Super Conqueror
HEP: leKpz M41, RU 251, Kpz 07 RH.
Premium HESH, pen is 120-130mm above average:
HESH: FV215b 183, FV4202, Centurion 7/1, GSOR 1008, Charioteer, Caliban, Conway, Chieftain Mk.6.
HEP: Currently there is no premium HEP-named shell in the game.
