How long (in rounds) would it take for a 10th level Human Fighter with 17 Strength, wielding a +2 Bastard Sword, with Greater Weapon Focus (Bastard Sword) feat, and with Power Attack feat to defeat this beast given the above declared 381 HP, 10 Armor Class, and Damage Reduction 3/Steel?
Chance to hit AC10: +2 (WF), +2 sword, +3 strength = +7 to hit. (Missing on a 1 or 2, or 10% for the first attack. Second attack missing on a 1-7, or 35% of the time)
I'd guess 8 rounds. If you want to include the possibility of criticals, I'd say 7.