These bullets were crafted by hunters as an easier means to stop certain types of monsters. In 14.01 Stranger in a Strange Land, one of the Apocalypse World hunters showed an assortment of these specialized bullets to Mary.
Silver bullets coated with a tincture made from holy oil, sage, and myrrh, followed by the recitation of a spell to mimic the original etchings. When used with the Colt, these bullets are capable of killing (nearly) anything.
Bullets dipped in dead man's blood. These bullets can be effective weapons against vampires, as they disoriented one of the masked vampires via headshot. When shot in the chest, the Sam of the Butch and Sundance Ending collapsed.
Hollow point bullets injected with holy oil. It is unknown the effect these bullets would have on an angel or demon as they haven't been used yet.
Hollow point bullets injected with witch-killing brew. These bullets are capable of killing witches who are otherwise invulnerable to traditional methods of dispatch.