Board Thread:Questions and Answers/@comment-31106929-20170402203126/@comment-26154973-20170403223729

They can do 20-60 (as well as up to 100), unless you have a combination of factors like bad ASW stats, bad engagement, low health, low ammo, or high armor target. It works like (positive part) $$( \overline{A \times B} \times C - D) \times A'$$, so to talk numbers you have to fully specify configurations (for attacker, battle, hit, and defender), then the damage ranges are deterministic.