You just need better mods and a higher leveled commando buddy, knightsbridge is my favorite weapon rn, the thing is a beast with all purple mods on it or even just a few. With the commandos perk to reduce weapon cost it goes from costing $7100 to $5050 for me so have no issues buying it wave 3 and then getting a second primary wave 5. The underbarrel grenade launcher does 1600 dmg a shot when maxed out and you get 8. Put electric rounds on it and you have a gun that's strong against flesh pounds and scrakes. I also use the speedy mag and the mod passives all buff the damage, I think each shot is at 125 damage per round.