I'm helping a friend fix his lvl 11 fighter battlemaster

greatsword +2

great weapon master

16 strength

so we wanna see what's the max damage on a round if he burns action surge and all his superiority die, and gets hew off of the GWM

so each attack with the greatsword is 2d6+9 (3 from stregnth, 4 from GWM, 2 from weapon)

he burns all 5 superiority die, each one is 1d10

so the max damage of 7 (2d6+9) + 5d10 = 197 damage a round max, correct?

Seems correct to me in theory. 

In practice, the actual effective damage may be lower if you take out enemies with some of the attacks — e.g. if an attack does 21 damage but the enemy only has 10 HP left, that extra 11 damage just kind of goes away, lowering the effective total amount of damage you're dealing to the enemies as a group. But if you're fighting one big enemy with more than 197 HP, then it would be possible to do that much damage on a turn this way.

Note that if you're playing 2024 rules and you use a +2 Greataxe instead, and you're fighting a group of closely packed enemies, you can increase the total damage dealt a little bit by using the Cleave weapon mastery (though it's limited to once per turn).

i just found out that the GWM bonus doesn't go off on that bonus hew attack. so 4 dmg less

Quote from babybabystewie >>

i just found out that the GWM bonus doesn't go off on that bonus hew attack. so 4 dmg less

Ah yes, you’re right, that only applies to attacks made via the Attack action.