Here's the fluff I created for them at our Warmachine meet up today. It can be used with just about any RPG system. I didn't preview, so I lost all of what I wrote so now here's the less cool version.
The Gun Mage:
Anyone can become a gun mage, because you see, they aren't really mages at all. The gun mage's gun is a work of science and sorcery and is highly unstable because of it. For this reason, gun mages wear special bracelets that inhibit any magic they possess. If the gun comes into contact with magic or is exposed to magic that radiates too close to it, it would be destroyed along with its user and everything within at least a 30ft radius. Even small spells such as illumination, when persisting over time and too close, will disrupt this weapon.
The barrel is enchanted with a permanent spell ward. A starting gun mage would spend at least 1,000 coin for the most basic gun. The basic gun looks similar to a flare gun with an enlarged and elongated barrel or small version of an elephant gun. The gun is made with a break-open style breech and uses a boxlock firing system. The "Spellshot" casing is usually made of copper and is sometimes enchanted with a spell ward as well. Inside the center of the casing is an iron rod surrounded by small supports. At the end of the rod, the tip of the casing, is the Spellshot - a solid sphere made of glass, usually mastercrafted, which is enchanted with a spell rune. When the mechanism fires, the rod is struck, causing the sphere to crack and release the spell down the barrel of the gun. The sphere is merely a housing for the spell and does not leave the casing. All "Casters", as they've come to be known as, are single-shot. Attempts were made to add barrels and and chambers but ended in failure. The act of firing these weapons in succession caused the same effects as spells cast in close proximity. Even firing two Casters too close together or too many shots fired within the same area would cause this. Although these guns are effective, they are still highly unstable.
Wizards that dare to take on the task of creating and selling these wares are "Spellsmiths". This occupation is a bit taboo considering the nature of the weapon. The danger of housing such fragile ammunition is great as well. Not only are weaponsmiths hard to find, they aren't cheap. Even a single 1st level magic missile could run you 10 coin. The larger the spell, the larger the gun. It needs to be large enough to house the spellshot casing. The price only goes higher. Some spellshot could cost you as much as 10 guns would have bought you. It's the price you pay for convenience and usually only considered by the wealthy or well-off.
