This item follow the great tradition of abusing, errr, useing magic to bring modern convieniances to a midevil fantasy world. Not as benign as the light spell cast at one end of a scroll case to act as a flashlight, the steam gun does place an out-of-balance amount of power in the hands of players.
The steam gun is really nothing more than a length of pipe with a hinge mounted handle. Unlatch the handle, tilt the pipe open like a breech break shotgun, and load in the ammo. Ammo is simply a small, potion sized container of water with a lead plug. The container can be made of metal, but is more commonly made of clay, ceramic or better, glass, due to their rust resistance.
When the steam gun is closed, it can be aimed at a target and the command word, usually “fire” in the tounge of the creator, is spoken. A varian of the heat metal spell with a shorter duration is activated and the ammo is heated to boil the water rapidly. The steam forces the plug out at great speeds and sends it hurtling toward the enemy.
The accuracy of the shot is horrible due to uneven pressure distrubution, smooth bores, plug imperfections and a host of other variables. Many players are aware of improvments like rifling and refined fuels, but be sure to thwart thier ideas with the simple question “And how does your CHARACTER know that?
Metal armour will provide protection against steam gun attacks, but mainly only at longer ranges when the shot is already likly to miss. Soft metal is used for the plugs because it can easily be worked into the desired shape.
If the players aren’t introduced to the weapon or see it in use, they may be quite confused by it’s function. A pipe with a handle that, if they can read the command word, heats up. In a seperate sack, the ammo pouch, a good number of clear potions, but none of them register as magical, being water after all. They made be induced to beleive it is some sort of smoking parephenalia, a camping tool to melt water, or even some twisted adult novelty.
When the command word is spoken, the chamber of the pipe heats rapidly to boil the water in the ammo. The ammo can be quickly converted to a non-lethal close range attack by removing the plug so a burst of steam shoots out. In addition to the metal plug, crossbow quarrels and grappling hooks can be loaded into the barrel of the pipe to be launched.