Talk:Rammus/Strategy/@comment-4641298-20120111105613/@comment-173.230.76.21-20120226064601

Thornmail returns 30% damage before reductions, and 30 base MR blocks only 23% of incoming damage.

With 380 armor (Thorn, Randuin's, DBC active, and base armor) you'll take 21% damage (100/(100+380)) and return 23% damage (.30*100/(100+30)) through Thorn Mail against an opponent with no ArmPen or additional MR. Not too shabby if they have 2 or more AD DPS'ers if you ask me.