I did a test last night, enough Anti Tank Rifle Companies to the value of roughly 1,000 men vs 1 King Tiger (maximum experience, leadership etc) and after about 30 minutes the King tiger had only an Engine, the Main Gun 88mm, the Coaxl Machine Gun and had lost everything else. The ground around the Tiger Tank was burning from all the rounds bouncing off of it.
So if you have enough Anti Tank Rifles then it can shut down even the heaviest of tanks, although in this case the king tiger continued to fire killing 300 of my Anti tank horde.