The Badaboom is better in almost every way. The Berrigan has less damage, basically the same accuracy, slower firerate b/c the Berrigan is burst fire and has a fixed burst delay, no luneshine, and 50% less mag size. The only way it wins is a faster reload speed.
And I think you can grind it only if you put a Berrigan plus 2 other legendaries in the grinder to get a Berrigan out.













