If I created a gun for World of Warcraft it would be legendary not epic. Guntitan would create it after he completed all the dungeons and quests that deal with the Titans and the creation of the dwarves, and got engineering to 450. Maybe even exalted with the Explorer’s League. He would need to study some serious ancient text hidden deep in Ulduar just to learn the schematic for it. All the mats for it would be located in Ulduar, too.
It would be available sometime after patch 3.1 when Stoneform becomes a permanent option for us dwarves.