Hmmm... Do you yourself have the B-1000? That is the only way to counter it. Unless with the  Solider's Sci-Fi ASR and the B-1000 has a Grenader weapon, that is really the two options I can think of.

Depends, what class you use. I've used soldier against him, i dont die much. You should probably keep jumping when he has BEARRAILGUN to make him confused wether to target up or down. And I reccomend you fight him when hes fighting with someone. Its best you counter his back secretly and meelee him, thats the best job for heavy or huggable