The following studies are of a theory that I have been working on for quite some time now and I hope that others either agree or see the flaws in it as that is what we need to do to find truth.
As the theory stands now it is my speculation that ALL weapons of sorrow require a living soul or an entity's essence or sorrow to be infused into the weapon for it to function to full capacity.
The three weapons that act as my prime examples of this are the guns Necrochasm, Touch of Malice and Thorn. The Necrochasm card says (dont quote me as i dont have it yet) that Edilon ally drinks of crotas essence to become Necrochasm. Touch of malice can only be crafted After you have obtained Oryx heart.
Everyone's favorite hand cannon Thorn I believe used the soul or essence of the noble man to empower it .
One exception to these is the failed weapon of sorrow Bad juju. so its my belief that this gun does not have a soul or it has not properly been infused into the weapon.
More evidence for my theory is the Kings fall raid guns as they are all associated with a person or a once living entity, one example is Chelchis Kell of stone as he might have been infused into the scout rifle Doom of Chelchis.
Well thats all from me for now, hope you enjoy.
Personally, I think Bad Juju should be a weapon of sorrow because it abides by the Hive's rules of killing making you stronger and was created with Hive secrets just like ToM, Necrochasm, and Thorn.