So I had an idea which is scary I know. But the khvostov is so ignored now that auto rifles are pea shooters. So I thought, why not let destiny know they should make it upgradable in the future. They did it with the necrochasm, the difference is people like this Gun. Old fashioned steel to battle the aliens.
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This was going to be in the original game. Sadly, they deleted it along with many other good ideas.