As topic says. I don't really understand what they're trying to say in the Dark Heresy rule book. Do the extra shots go to the same person? people behind/adjacent to the target? Do the extra shots use up extra ammo, or are those supposed to be extra pellets? what if I'm firing at long range ( >20m)?

30m ranges

PBR<=2m<SR<15m=MR<=60m<LR<= 90m<ER<=120m

I don't think scatter has changed from dh to rt, but in rogue trader scatter weapons work like so.

A scatter weapon only causes additional 'hits' when fired at point blank range (PBR). The additional 'hits' are scatter from the shot which is essentially the target getting hit by additional pellets as you mentioned. So in a way scatter works like righteous fury no additional ammunition is expended but the shot does additional damage.

Because of the way ballistic skill tests are made (a single roll) scatter from one round is the same as scatter from five rounds (something like an assault shotgun) and doesn't increase with the expenditure of additional rounds.

From short range (SR) out to medium range (MR) a scatter weapon does its listed damage with no scatter.

At long range (LR) and extreme range (ER) the weapon does its listed damage with all armour protection against the shot doubled and no scatter.

This means shooting a person in guard flak AP4ALL with the shotgun (range 30) at 0m-60m reduces the damage by 4 points per hit. Shooting the same guard from a range of 61m-120m reduces the damage by 8 points per hit (long and extreme ranges).

Hope this helps.

Edit: These range numbers might be slightly different in DH check the errata or the book for further details.

As for spread it stats scatter hits more of the target and to refer to the multiple hit table on pg 190 DH CR.

PBR is 3m, not 2.

an example:

Thog, our brave Guardsman wields a Vanaheim (Assault shotgun with Full Auto) and has a BS of 50

He is 3m away from the victim he intends to shred to pieces. After all it is a cultist, a beggar, a democrat or something similarily evil.

Full auto adds +20 to the shot, Point Blank another 30. so he rolls on a 100.

He casts the dice and gets a say 20. the Vanaheim has max full auto of 6, so he scores all six hits. And at the same time scatter kicks in where he gets another hit for each 2 DoS. He has 8 DoS so 4 more hits. in total he scores 10 hits against the victim while expending 6 shots (full auto burst with a Vanaheim)

But though luck, the victim was a High Level Throne Agent who is wearing Powerarmour and has more Thoughness then a tiny Space Marine and laughs about those 10 hits, which is what happend in my last session

That is a nice and detailed explanation of the scatter mechanic. Thanks all. And currently my shotgun only fires 2 shots, but I think I will have the opportunity to upgrade it to 4 shots. Our GM made it up, it does 2d5+3, Pen 0, Impact, 30m range, 8 shells loaded, fires - / 2 / -, that is, both barrels at once, reloads a t 2 full, which is 1 full with quick reload, and even a half action if your GM rules you can use a quick loader and it halves reloading time, and it's called a Veldoran Pattern Combat Shotgun. It can loads shells individually from the top or it can use a round quick loader underneath. Sometimes it just fails miserably and does about 4 damage against tough enemies, and sometimes it goes mad and does 30 damage to one dude. I'm starting to grow fond of it!

Schwarzie said:

But though luck, the victim was a High Level Throne Agent who is wearing Powerarmour and has more Thoughness then a tiny Space Marine and laughs about those 10 hits, which is what happend in my last session

There is a saying about going to a gunfight with a knife...