What guns are worth firing AP out of and when?

[QWERTYEel89]

I hear 152s are crap for that I definitely wouldn't be surprised at anything above tier 5. But, what other factors should I take into consideration besides a ships tier/type.

[Fast_Battleship_Iowa]

Shell velocity and caliber.  Unfortunately, velocity is sort of a "by-thumb" experience, but in general 203mms and above are worth firing AP out of at the FLAT SIDES of heavy cruisers, battleships, and (when it happens) aircraft carriers.  For the love of the sea - don't jump the trigger.  Wait for a good angle of fire, otherwise your salvo is going to be not-so-good.

[MrDeaf]

152mm AP, from Omaha and Cleveland, will penetrate and citadel...

Aoba, Omaha, Pensacola: under 9km from flat side. About 7~8km at angle

Kuma, Furutaka, Atlanta: About 10~12km

Cleveland: Around 7km, assuming you can hit the ridiculously small hit boxes

 

I haven't had too many close encounters with a Myoko or Atago, so I can't say much about those.