More reserve ammo, I think it would be the best primary in the game.
High damage output, high stability, fully auto, and what a lot of people don't seem to realize is that it bypasses all enemy shield types (yes, even arc and void shields).
Only drawback is the damn thing is an ammo whore. But other then that, the gun is amazing. Doesn't get enough love in PvE IMHO.
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I use it on my warlock with special weapon focused perks. Mainly the ones that increase special weapon ammo. For example, two of the sunsinger exotic chest pieces have perks for more special ammo and the trials boots for warlocks will carry more special ammo as well. That fixes the problem for me.