Strategy - Advancing against very strong AT Guns

[Shad]

The thing to remember about AT guns, however ferocious, is that they can only fire once per turn. This means that if you carefully consider ranges and avoid overlapping fields of fire you should be able to overwhelm them in sequence by presenting more targets than they can handle at one time.

If INF is screening the guns you will have more difficulty. In the setup you posted I would make every effort to wedge through the infantry line at the far left and overrun the single gun, then roll up the flank. This way you are only exposed to one gun (or one + a long distance half strength shot) at a time.