@JeremyECrawford do half orc savage attacks crits and barbarian brutal critical hits with a greatsword use both d6 again or just one?
— Derrick (@Scyllan8) June 6, 2016
Savage Attacks and Brutal Critical both let you roll one extra die. #DnD https://t.co/Vu0pQaIwH9
— Jeremy Crawford (@JeremyECrawford) June 11, 2016
I think the question may resolve around the fact that a Greatsword does 2d6 while a Great Axe does 1d12. A lot of posts say that you only get to roll one extra die when you critical. So there is a huge advantage to a great axe adding 1d12 while the greatsword would only add 1d6.
But the PHB says that when you score a critical hit, you get to roll extra dice
for the attack’s damage against the target. Roll all o f the attack’s damage dice twice and add them together. Then add any relevant modifiers as normal. To speed up play,you can roll all the damage dice at once.For example, if you score a critical hit with a dagger, roll 2d4 for the damage, rather than 1d4, and then add
your relevant ability modifier. If the attack involves other damage dice, such as from the rogue’s Sneak Attack feature, you roll those dice twice as well.
That seems to say that the great sword would roll 2d6 on the critical as well as the normal hit. Are you saying it is indeed only 1d6?
No,that is just about the brutal critical ability Barbarians receive at level 9. “Basic” crits follow the rule you stated.