Okay a Devastator uses a full auto attack he gets six hits, on two he gets a 10 on 4 of the damage rolls. I imagine you just give the devastator 1 new attack instead of four separate ones

You works out each hit individually.....

So with six hits you roll six damage rolls with each one chance of rightious fury which adds to the damage

See page 245, but to elaborate:

In your scenario, if he got a 10 on 4 of the 6 hits, you would roll 4 additional BS tests to confirm RF. For each success, the roll damage again (2d10+10, in this case) and add it to the previous total. It is not an extra hit, so you don't subtract Toughness and Armor twice, and there is not an additional hit for Unrelenting Devastation (or similar abilities). If one of the damage dice in the RF damage total comes up as a 10, you roll another set of damage dice and add it to the current total without retesting BS a second time. That continues until no 10 is rolled on the damage dice.

It's not specified in the RAW (that I saw anyway), but I think it's generally agreed that you can't get more than one RF per damage roll. So, if you shot a lascannon and rolled 5 10s on the initial 6d10, you would only roll for RF damage once, not 5 times.

The way I have it for my players is any die that comes up a 10 can trigger RF, but only for that die. This check is limitless, so if they keep rolling 10s, they can keep checking for RF, but only on that die. So, if they are rolling 2D10, and both come up 10, they check for die seperately, and all dice are totalled together once they stop rolling 10s.

In the case of special abilities where they're rolling an additional die, but only keeping the original number (ie, roll 3D10, keep the best 2), the number of RF attempts for each round of checks equals the keep number, not the roll number (ie, in the case above, only 2 rolls that came up 10 get to check for RF, even if all 3 dice come up 10).

Kabal said:

I agree that this makes more sense (and that's how I would rule, were I the GM), but the RAW says a whole new damage roll. It does make for disgusting damage totals for lascannon hits though (~46% chance to roll at least one 10 on 6 dice).

Radomo said:

Yop, the rules say if you get one or more 10s on a damage roll, you get to roll RF. I interpret this as 1+ 10s = 1 attempt at RF. It also says "this process continues so long as one damage dice results in a natural 10" so RAW says if you roll a 10 and a 4, you reroll and add the results. If the next roll you get a 10 and a 10, you roll RF again.

Something I did notice was the example text differes slightly from the rule text- the rule text implies that you continue to re-roll dice for damage, but the example indicates that you roll dice and add any applicable modifiers, which results in considerably more damage. My group has tried both, but without adding the bonuses to damage, firearms tend to rule the day a bit too much.

RF was never a problem for our group in DH, as often you needed the extra damage to survive. But from what I've seen via bolter porn in DW, even your elites will get wasted in a hurry...I kind of like the HR of making only the die that comes up 10 explode...

Charmander said:

This may be poorly illustrated in the book, but the example does not differ from the rules text. The rules text is using the term Damage roll . Damage roll is not to be taken wordly, as in: "only the numbers you roll", it is a term. It is the the act of calculating the damage an attack deals, before the result gets passed over to the defendig player (or GM) to be further modified (cover, armour, TB,.... <- Defensive modifiers) and applied onto the victim.

It´s a term, named after the iconic action a player performs when calculating the damage his/her figure does (rolling dice). Defensive modifiers don´t get applied by the attacker but by the defender, thus are not part of the Damage roll. With that in mind the example is absolutely accurate and frightening, batshit hardcore, I might add.