Using xNormal, an ancient piece of software, I baked the high-poly model to get its bump map for export.
The normal maps
Next, I exported the low-poly's UV map to Photoshop, and applied bright colours to differentiate between different materials better when it arrives in Quixel.
The low poly currently makes Super-Soaker's look manly.
Using Quixel Suite, also known as 'Loading Screen and Crashing Simulator 2015', I changed it from a gun for clowns and childrens birthday parties, to this:
Next, I brought it into Unreal 4 to properly present it.