Available till tomorrow @ 8pm EST.
Corkscrew/Armor Piercing - Reconstruction/Hatchling
Reconstruction is very good, especially when dealing with Champions. Less worry about not having ammo to pop a barrier. Hatchling will hopefully get better with threadling buffs coming in the near future.
It works best on very large or very small mags. Primaries all have medium size mags so simply reloading them is much faster than any alternatives.