Mechanically it doesn't really matter if you are using a Colt 1411, a Glock, or an old german Luger, they would all have very similar profiles so call them what you want. Use the following Guidelines for building them on your own pending my approval, generally if what you are doing makes sense then my seal of approval should be easy to get.

-Guns use the Archery Weapons Profile.
-They come in Light, Medium or Heavy varieties.
--Ok, so what makes a gun Light, Medium, or Heavy is a little tough. Basically I have to leave enough room at the top for your Rambo Dawn Caste to have his M-60. What it comes down to is this. Most Guns will be Medium. Small Pistols and .22 rifle are Light. High caliber (Sniper Rifle, Rocket Launcher, .50+) and High fire rate moderate caliber (Miniguns, not Uzi's) are probably Heavy. Basically stray on the side of Medium unless it is pretty obvious that it should be Heavy or Light.
-Adding the Guns Tag to the game to go along with that Ability, it works basically like the Archery Tag. Understandably Guns have it.
-Most Guns are Guns (Long), Pistols are probably down to Guns (Medium), Derringers, real Flame Throwers, and Sawed-Off Shot guns are probably Guns (Short).
-Guns Have the Crossbow Tag
-Guns Have the Lethal Tag (Special Ammo can change this to Bashing)
-Precedent based on the Flame Piece indicates Pistols should have the Mounted Tag
-Shotguns have the Powerful Tag
-Light Pistols probably have the Concealable Tag
-Some very large, very Small, or very old guns could have the Slow Tag, but most do not.
-Most Pistols have the One Handed Tag.
-Guns are Piercing against mundane primitive armor. Armor Piercing Ammunition gives the Piercing Tag

Some Examples
.38 Special
Light Gun Weapon
+11 Damage, 1 Overwhelming
Tags: Lethal, Guns (Medium), Crossbow, Mounted, One Handed, Concealable

Sawed Off 20 Gague
Medium Gun Weapon
+13 Damage, 1 Overwhelming
Tags: Lethal, Guns (Short), Crossbow, Mounted, Powerful, One Handed

.50 Cal Sniper Rifle
Heavy Gun Weapon
+15 Damage, 1 Overwhelming
Tags: Lethal, Guns (Long), Crossbow, Piercing

Colt's Gun
Artifact Colt 1411
Medium Gun Weapon
+16 Damage, 4 Overwhelming, 5 Attunment
Tags: Lethal, Guns (Medium), Crossbow, One Handed