Wouldn't strength only need to get to a certain "good enough" point rather than "as strong as possible?" Maybe the shell is already at that point? And after tha

Wouldn't strength only need to get to a certain "good enough" point rather than "as strong as possible?" Maybe the shell is already at that point? And after that point, maybe all there is left to concern yourself with is how it behaves in an explosion. As with any thing designed to explode (grenade, bomb, etc.) Maybe they want for the thing to come apart in a certain way rather than holding together?