just a heads up, i've tried this thing out, and noticed a few things you should know before using this weapon
1.) you DO NOT have to get precision kills, or kills at all, to activate the SIVA - however, precision kills will automatically trigger the full effect - body shots will slowly build up the swarm
2.) you CAN NOT use the swarm infinitely, when you gun no longer glows with swarm, it means you cannot use the special effect, the cooldown is quite fast, but do not expect to kill an entire 20 pack of mobs with this gun with concurrent head-shots
3.) SIVA is not your friend, it is not your ally, much like the health stealer counter perk of Touch of Malice, this weapon WILL HURT YOU if you get too close to the SIVA clusters, meaning this gun WILL ATTACK YOU if there are no more enemies and the clusters are still active
:)
cheers, and enjoy your hard earned OUTBREAK PRIME