I don't care if it's the M1A2 or Challenger 2, even a near miss from a 460 mm shell will do significant damage to a main battle tank. The treads could be wrecked, the main gun damaged, etc.
A High explosive shell of anything larger than 180mm will probably kill the crew if the shell expodes on the tank, under the tank, above the tank, or to the side of the tank and maybe even the front. Modern Battle tanks dont actually have that much armor on the sides and so they reinforce it with add on armor like ERA or NERA that can bolt on fairly easily. That is just a basic explanation, as there is much more too it. The side of a T72 is around 80mm without counting the side skirt (as it adds very little) and could easily be penetrated by any tank from WWII with more than 80mm of penetration, which is pretty much most tanks including the short 75mm sherman and even some 37mm cannons. However with add on armor it can increase the protection, so for example it increases it to 100mm, which is still not much but enough to protect from most small cannons. However that is not where most add on armor shines, most add on armor now a days is mainly for adding chemical protection, which protects against munitions that rely on explosives to penetrate like shaped charges. Though a 46cm, which is about 18.1 inches, would most likely hullbreak a tank as the shear weight of the round and its speed would crack open the tank like a empty soda can being hit by a hammer.
