Before I answer. You’ve entered the wrong forum. Off topic is for stuff that has nothing to do with the game. You’re best bet would be to edit this post and move it to destiny2 or to lore.
Wave splitter and cold heart seem most likely to me.
ColdHeart technically shoots a supercooled liquid coolant, but I don’t know how you would keep it cold enough for that long a period of time.
Wavesplitter however shoots sound waves, which seems much more feasible to create than the others. However, you would not see the beam(ignoring synesthesia) that comes out of the gun, and finally instead of disintegrating whatever creature you are firing at, you’d most likely crush it/ knock it back with the force equivalent to an Apollo space shuttle headbutting you.
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MenthyeSpace Pirate extraordinaire - old
But coldheart is cold fusion powered isn't it? -
If I remember right cold fusion in real life is strictly theoretical.