Find yourself a good masher, with good RoF and a high-powered scope.
Use a gunslinger mod that at least has + to whatever that crit dmg thing is...deadly I think it is.
Ignore the stupid bird - it's retarded. I got tired real quick of picking up purple grenade mods and piles of money I didn't need.
Spec down sinper and gunslinger. Ignore all proc skills (save for the last one in gunslinger, the pirate thing)
By 55 waste 5 points in the bird so you can unlock fast reload.
(why that skill is under bird I have no clue...predator should be under bird and fast hands should be under gunslinger?)
Scoped masher + tresspass = free exp.
I mixed and mashed (hehe) things up and found this combo utterly destructive.