270mm

Tier 10 meds have around 260~270mm penetration on standard ammo.

430u's "weakspot" that's 5 pixel tall has that much armor when you hit it flush on. Also its upper plate. You have a 50% chance to pen it with a tier 10 medium shooting standard ammo.

Or you can just load HEAT and autoaim at the tank. Will pen 8 out of 10 times.

It's armor that's a bit higher than 270mm which forces you to shoot gold if you don't wanna at best coinflip every shot you take.

This is what frustrates me the most; shooting standard and relying on RNG to pen even well aimed shots or shooting premium and pretty much reducing the need to aim. Both are not fun at all, but have no choice to shoot gold if you want to deal damage.

And there's quite a few tanks that force you to coinflip or load gold. (Type 5 being the biggest offender)