These bullets were designed by hunters to kill more high level 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 anything.
Hollow point bullets injected with holy oil. Despite not being used yet, they can debilitate or kill monsters vulnerable to holy oil, such as angels and demons.