The recipe for this item is taught by Goblin Engineering trainers.
The gun can explode at any time during use, dealing 100 damage per second and forcing the caster to run in circles for the remainder of the 10 seconds.
The 61-69 damage is not total, but rather per second. This gives a maximum damage of 690 over ten seconds in a cone.
The gun can still be used if you later drop engineering, as it does not require engineering to equip or use.