Here is the build I use, even though it must be far from optimized :
My goal is to buff iron bear as much as possible, and to not be useless outside of it. This is why I picked Drowning in brass for the added damage for me and my friends. You can also take Experimental munitions for more dps, but I prefer To the last as it is very useful in terms of survival. You can also take points out of Drowning in brass and put them in Explosive ponctuation to reduce the cooldown of IB, but I don’t really use splash damage outside the mech and I find the cooldown is good enough as it is.
You can also move the point in Means of destruction to Pull the holy pin for more damage.
I use double missile launcher without augment most of the time for iron bear. In coop, I like to use the target softening augment on one launcher for tough bosses, especially in M4 and for the Takedown (+15% damage for the team). When I know i will fight nimble enemies, I also like to put homing rockets or the explosive minigun as they are really good for tracking fast targets.
When it comes to gear, you can use the weapons you prefer depending on the situation and the enemies you face. There are only 2 pieces I consider really important : the class mod and the artifact.
I use the new class mod that drops from Billy the annointed in M4. It took me something like 5 hours to get it, but it is absolutely worth it :
If you want to farm Billy, I would advise you to use a fire cutsman as it absolutely shreds this boss because of its big hit box. A fire lucian’s call, lyuda or night hawkin work well too (especially the lyuda, although the ammunition can be a problem).
I chose my artifact because of its stats, even a blue one with the right ones will do :
The health and movement speed are a nice bonus, as is the damage increase against frozen foes, but the added area damage is what makes this piece of gear great. I tested it on the target dummy in sanctuary, and I found that the bonus is multiplicative and applies to IB splash damage (missiles, explosive minigun and grenades). With all the recent buffs to IB through better scaling and talents, the mech is now really tanky (I can pretty much facetank everything in Maliwan takedown in M3, even in the middle of crowds of enemies, as long as I keep hitting with my splash damage ; I haven’t tested M4 yet) and the damage is really nothing to scoff at. I melt pretty much everything in M3, and for now it still holds up even in M4, even though i wouldn’t depend only on IB for really tough badasses and bosses.
Hope it helps =)