I have done onslaught many times, and even though I have been mostly focusing on one weapon, I have not obtained some rolls, but got certain rolls two, or three times, others, not even once. I was hoping for destabilizing rounds, with onslaught, and armor piercing rounds, not happening, I did however, get destabilizing, AP, and tap the trigger once, though, and destabilizing, with flared magwell, and another with ricochet rounds I got some unexpected good rolls too, for weapons that I wasn't even focusing on, or hoping to get, it took a loooong time, and many tries, definitely an abysmal experience, if you just want to pick up a weapon, and start playing with it.