This gun is not only available in the demo, it is not only available to low level either. I obtained the Husk of the Pit in the full game, while playing as my level 31. Read the description of my video and you'll see how I got it. If you want proof that I have it, SEND A MESSAGE TO INSANEBIKER118 AND I WILL INVITE YOU AND SHOW YOU.
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Got it the other day. Spent about an hour and a half in the Cosmodrome farming Blades, but it dropped eventually in the Rocket Yard. Obtained on my L30 Warlock. Low level and demo not required.