Modder xxdeathknight72xx found the weapon, which replaces the Railway Gun if you have it in your arsenal (or use cheats). Interestingly, a bubble animation surroundings kill, suggesting Bethesda might have envisioned an underwater sequence in Fallout 4. The video's host, Tryannicon, also surmises that it's possible this weapon may be featured in Fallout 4's upcoming DLC and wasn't mean to be found just yet.
Mods Link: http://www.nexusmods.com/fallout4/mods/1619/?
Cheats for Fallout 4: h
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