There isn't any sort of rule dictating that they aren't allowed, as far as I know. As long as it isn't fictional, I guess, yes?
Wuzh wrote: Are directed energy weapons allowed on this wiki?
Okay, I'll leave this to your interpretation:
"On this wiki, a gun is defined as large arms from 1331 (cannons) to the mounted guns of today (artillery and armored units, aircraft and ships) and small arms from 1418 to today (pistols rifles, muskets, shotguns, mortars and RPGs). Another way to view a gun is a metallic barreled device that propels a metallic project; explosive or not. This would also include articles containing information on a gun's cartridge, shell or ball.
This means Gun Wiki should not include any articles that are relating to such things as rockets, grenades, mines, missiles, ICBMs, Armor, Aircraft, Ships and explosive devices in general. Such articles will be promptly deleted. Weapons with a name that include the word “gun” like electroshock gun (taser) as well as fictional guns (phasers and laser weapons) and especially toy guns are not fit subjects for this wiki."
If it's a small arm designed for lethality, I'd say it qualifies. Defining a gun as exclusively something that propels a metallic projectile is a bit of an oversight since there are rare exceptions. I'm guessing the "metallic" bit was just thrown in to stop people making pages about BB guns.
What do you think?