"My damage was so high that I, for the first time ever, saw the damage proc 'Total Existence Failure'," NickTew explains. However, "you basically don't need anything for this to work other than a gun" and a bit of bonus gun damage. Playing Vex, NickTew explains that he only has around 25 of the 49 skill points the game gives you for some spare gun damage. Best guess I have is that the explosives start using the taser's damage modifier instead of the SMG's base damage the moment NickTew swaps over. Add in the Sticky magazine's escalating damage and other skills, and you get within that 300,000+ damage ballpark.