easy thing, go chain reaction, wrecker, stick at least 3 bombs per detonation, go Royal Decret 4 or 5, use your grumpy while he's shooting, while he activates Juggernaut, he shouldn't be able to escape, if you can stick more than 3 bombs, better.
NEVER stay at close range when fighting Mal'Damba, try staying at a confortable distance where he cant easily hit or stun you, and you revolver has the advantage.
Look out when he is loading his salvo, use reversal and intentionally go into where he is shooting to maximize the reversal effects either at him or another enemy with lower HP to instantly kill them.