In my current group I have a Tactical Marine player and a Librarian player both with the Death is Joy armor history and they are turning hordes into bloody pulp. They do this simply by unloading on hordes with a standard bolter on full auto fire. Has anyone else run into this and do you have any solutions on how prevent them from slaughtering hordes too badly?

It states any successful attack is +1 to horde magnitude damage. I'm unclear why that is causing issues. IF you misread it as each HIT is one extra damage to a horde then I could see where you might have a problem.

For example a marine using full auto is one attack. Period, no matter how many successes are generated that is one attack.

Then I totally misread, thank you for the clarification.

No worries, I usually tend to read things as they are and not replace words in the Deathwatch text. Huge post about medicae skill from people not taking the literal meaning of wounds under first aid.