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wad

A wad is round piece of material, usually cotton or plastic, that separates the cavities of a shotgun shell. For example, there are usually wads separating the powder charge and the shot, and sometimes a wad on top of the shot pellets to keep the crimp from deforming them. Some manufacturers add fins or other aerodynamic features to the wadding to help it keep the shot in a group for a longer period after it leaves the barrel, improving the group size at range.

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wax slug

A wax slug, like a cut shell, is a method of improving the lethality and accuracy of birdshot shotgun shells so that they can be used for hunting larger game. To make a wax slug, the crimp holding the shot inside the shell is opened and wax or some other hardening liquid (glue, epoxy resin) is poured into the shot until the shot is submerged. After the liquid hardens, the shell is crimped closed again, and the wax slug is ready to be fired.  

Wax slugs do not have the full accuracy or penetrating power of true shotgun slugs. However, they are an effective emergency hunting round, extracting power and accuracy from even the most inexpensive shotgun shells.

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wildcat, wildcat cartridge

A wildcat cartridge is a cartridge that is not officially recognized by SAAMI or CIP. Wildcats are usually developed to fulfill some niche shooting role, or to hold some sort of record such as highest-velocity or flattest-shooting cartridge in the world. In some cases, wildcats become officially recognized cartridges and enter large-scale production, and one could argue that all cartridges are wildcats at some point in their lifespan. Still, the term "wildcat" is generally reserved for hand-made cartridges with no large-scale production. As such, most wildcats are exclusively the prerogative of custom gunshops and eventually fade into obscurity.

Some notable wildcats, a few of which are now well-known cartridges, include:

.22 Eargesplitten Loudenboomer 
.300 Whisper
.30 Shaman
6.8mm SPC

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