For context, they managed to successfully accomplish an impossible task (defeating a Lich with it's minions) to save their tribe's armoury and magical item stash. So their master, an Ancient Red Dragon, will give them an item from his own collection
Does it have to be from D&D? Because there's a blood-fueld submachine gun that does fire damage in a GURPS supplement and it's, uh, totally in line with my backstory.