Since Blizzard are being really cool and have published reference kits, getting blueprint for the gun was quite a breeze. I just scaled this picture to fit my hand.
The build itself was based around using what I already had, cardboard tubes, bottle caps, and foam. The foam was carved using the scaled blue print as a guide. See Kamuis videos for a more detailed guide.
To bring the gun to life I added paint, weathering and some warning stickers.
And since I now know how to make mini smoke machines I really wanted the gun to emit "frost smoke". I followed Valkyrie Studios tutorial while making the smoke machine.
The final result
Photo by Cosplay.studio