Given that a number of people feel the "reroll if you roll a 1 or 2 on a damage die" bit can slow things down, is there any solid mathematical reason not to change that to "treat any rolls of 1 or 2 on your damage die as if you'd rolled the average for that die"?
I know it's not going to average exactly the same, but am I correct in thinking it ought to be near enough for most practical purposes? Do you see any hidden downsides? (I'm foolishly posting this after 4 AM, so if I'm overlooking anything blatantly obvious, I blame sleep deprivation.)
I think you're on sound math doing this. I mean if you were running the probabilities, you would assume a statistical average for the re-rolled damage dice anyhow, wouldn't you? I think the maths are more complex than I'm making them, but I’ll do my best. Note: I am not a professional statistician.
The only question is if this gives an unfair advantage to certain weapons. I'm thinking greatsword/greataxe (2d6 damage, avg 7, so rolling a '1' isn't possible) vs. a reach/versatile weapon (1d10 damage, avg 5.5).
According to my dirty maths:
Great Weapon Expert with greatsword/greataxe gives you a net +0.2777 damage bonus per round.
[SBLOCK=Greatsword/greataxe Maths]
Let’s say your average PC taking the Great Weapon Expertise feat is likely to use a greatsword or greataxe which deals 2d6 damage.
The odds of rolling a 2 (1, of course, is impossible) on 2d6 is 2.77% each time you roll.
Usually we do DPR (damage-per-round) calculations for monsters over 3 rounds, so let’s do the same here. Also, let’s assume that the character with this feat is making two attacks per round, so either they are 5th level with Extra Attack, make an opportunity attack, or have haste cast on them; I think that’s a pretty reasonable assumption.
So two attacks per round, over the course of 3 rounds - what are the odds of rolling a 2?
2.77% * 6 = 16.62%
This means that in about 1 out of every 6 combats (which we’re assuming last 3 rounds each) you’re going to see a 2 rolled on 2d6 (statistically speaking).
And we’re going to assume that when you re-roll your 2d6 you get a statistically average result of 7.
Which works out to getting a +5 bonus to damage (from a 2 to a 7) once every 6 combats, or once every 18 rounds.
And that works out to getting a +0.27777 bonus to damage each round.[/SBLOCK]
Great Weapon Expert with a reach/versatile weapon gives you a net +0.26666 damage bonus each round.
[SBLOCK=Reach/versatile weapon Maths]
Now the same situation, but they’re wielding a reach weapon or a versatile weapon in two hands which deals 1d10 damage.
The odds of rolling a 1 or 2 on 1d10 is 20%.
So two attacks per round, over the course of 3 rounds - what are the odds of rolling a 1 or 2?
20% * 6 = 120%
This means that in 1 out of every 5 combats (which we’re assuming last 3 rounds each) you’re going to see a 1 or 2 rolled on 1d10 (statistically speaking).
And we’re going to assume that when you re-roll your 1d10 you get a statistically average result of 5.5.
Which works out to getting a +4 bonus to damage (from a 1.5 to a 5.5) once every 5 combats, or once every 15 rounds.
And that works out to getting a +0.2666 bonus to damage each round.[/SBLOCK]