My group ran into a few thoughts on the rules when we came to the Combat Shotgun

First thought was do additional hits from Autofire, Scatter, and Semi-auto stack to the standard damage roll? (ex. Our Arbite fires his autogun on semi-fire. Hit gets four degrees of success. Would he do 3d10+3 damage or would he do 1d10+3 three times??)

Second thought. Does the Scatter act like Semi-auto??

and last was a combat shotgun. How does that work??

Each hit is resolved individually. There is only one exception to this in the form of a Xenos weapon in one of the books.

So, for example, you managed to score a total of 3 degrees of success on a full-auto burst, you have 4 total hits; 1 for basic success, 3 for extra degrees. Each hit's damage is rolled separately with armor and toughness applying to each in turn. There's even a little table on page 190 of Dark Heresy ( Table 7-6: Multiple Hits ) which speeds up determining where the extra rounds impact on the target.

-=Brother Praetus=-

So that answers my first thought. Anyone able to help me understand scatter abit better and how combat shotguns with scatter and semi-auto work?

Scatter works just like semi- / full-auto where each hit is resolved individually.

Also to help you understand how the two work together, read this taken from the errata

The Actions section starting on page 190 should include a special note concerning combining semi-auto and full-auto fire with the Scatter quality, which reads "When firing a semi- or full-auto burst at point blank range with a weapon that has the Scatter quality, the extra hits for rate of fire and scatter are worked out separately and both applied. For example, Horatius Kane fires his combat shotgun at Heretic X. Kane is at point-blank range and fires a semi-automatic burst. Kane rolls 01 with his modified Ballistic Skill of 70 (30 BS, +30 for point-blank range, +10 for firing semi-auto) and hits by an amazing six degrees of success. He gets one hit at 70, one hit for semi-automatic at 50, and a third hit for semi-auto at 30 (he does not get a fourth hit at 10, because the combat shotgun's rate of fire is 3). He would get additional hits for scatter at 50, 30 and 10, for a total of 6 hits on Heretic X, most likely shredding the cultist to bits in the Emperor's name.

Thank you both very much for the help. We are on our first run through (Kinda sad cause i got the books before Fantasy Flight Games bought the rights) and that is the main things we ran into