The Literal Silencer: This accessory makes the firearm that it is fitted to *completely silent*. In addition to silencing the gunshot, it eliminates associated noise. The bullets will not generate a "crack" if they break the sound barrier, nor will they make noise if they hit anything. The gun's action noise is silenced. The empty casings will be silent if they hit anything. If the gun is dropped or struck, there will be no sound.
Omnivolver: This revolver can safely chamber and fire ANY handgun ammo(percussion, electric, or any other ignition). You may mix and match calibers freely. It can hold 6 rounds of roughly .32-.45 cal. You will gain some capacity with small-caliber rounds such as .22LR's. You will lose some capacity with large-caliber rounds such as .500S&W Magnums or your own personal .67 "Ouchmaker" handloads.
Ubershotgun: This looks like a 10 gauge double-barrelled shotgun. It is actually designed to fire 20mm cannon shells. Through magical means, the recoil is reduced to a normal shotgun level.
I can't think of a name for this one: This gun(of whatever type) is enchanted so that its bullets(or pellets/slugs for shotguns) will do at least half damage to anything that would otherwise be immune to them. For example it would do at least half damage to any creature with one or more of the following powers: immunity to non-magical attacks, immunity to metal, silver required, "plus" whatever required, left-handed redheaded plumber on a Tuesday required. Its shots will do full damage to anything that is affected normally by normal bullets.
Very High Capacity Magazines: These mags appear normal, but they contain a dimensional warp that allows them to hold three times the normal amount of ammo without increasing the weight beyond normal. Fixed mags may also be enchanted with this ability.
Magazine of Teleportation: This appears to be a normal detachable magazine. It is sold with a box that is about the size of a shoe box. The magazine cannot be filled in the conventional way. However, it will teleport ammo from the associated box to the feed lips and feed it normally into the firearm. This works from any distance. Cheaper versions could have reduced ranges between the storage box and the mag. Fixed magazines could also be enchanted with this ability.
This is not the gun you are looking for: This is a popular enchantment for "Evil Assault Weapons". It makes a "scary gun" look politically correct and lawfully owned. "Oh, my mistake, it's just a skeet gun after all."
Duplex rifle: When this rifle is fired, it magically consumes an extra round. The consumed round is not recoverable, and no extra casing is ejected. The bullet from the fired round has its range and damage multiplied by 1.5. The rifle may be set to fire normally as well.
Martyr's Gun: The firer can choose to take any amount of damage when he fires this gun. The same damage also affects the target, and bypasses all armor, protection, and immunities for both parties. This is in addition to any damage from the gun's projectile(or beam, for energy weapons).
"Newton's Mod": This enchantment gives a gun the range and damage of a more powerful caliber, but it increases recoil to the level of that caliber. For example, you could enchant an .223 rifle to have the range and damage of a .300 Winchester Magnum, but it would also have that level of recoil.
Sound Transmogrificaton: This enchantment causes the sound of the gunshot to be changed to an equivalently loud word or sound effect. For example, a gun could be enchanted to actually say the word "BANG" when fired. Other popular effects include "ZAP" for energy weapons, "FREEDOM", "HA", "OOPS", drum rolls or flatulence noises for full autos, etc.
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