A bullet was a projectile propelled by a firearm. Most bullets were made from a type of metal.

In human mythology, bullets made of silver could be used to kill a werewolf. A "real" werewolf like the Lupine Wavelength Haemovariform was unharmed by ordinary bullets; as the Tenth Doctor said to Captain Reynolds, "Bullets can't stop it." (TV: Tooth and Claw) Silver bullets were also utilised by the Brigadier to defeat the Destroyer. UNIT also used teflon anti-Dalek bullets and gold-tipped bullets for use against Cybermen. (TV: Battlefield)

The Cybermen of Pete's World proved invulnerable to bullets, (TV: Rise of the Cybermen, Doomsday) as did Ice Warriors. (TV: The Seeds of Death)

The Experimental Prototype Robot K1 was immune to bullets much to the frustration of the Brigadier, who commented "just once I'd like to meet an alien menace that wasn't immune to bullets." (TV: Robot)

In the Sontaran invasion of Earth in 2009, the Sontarans used a cordolaine signal excited the copper atoms in bullets and caused their expansion within a gun barrel, rendering Earth-made guns useless. The Doctor admonished General Staal for this, stating that "a Sontaran should face bullets with dignity". UNIT managed a counter-measure by using rad-steel coated bullets. This made the cordolaine signal ineffective and the Sontarans, despite their use of Sontaran space armour, were easily defeated by UNIT forces. (TV: The Sontaran Stratagem/The Poison Sky)

During the 21st century Dalek invasion, the presence of the time-lock within the Hub became apparent when the bullets fired by Gwen Cooper and Ianto Jones against a Dalek were suspended in mid-air. (TV: Journey's End)

Bastic bullets were used to destroy pre-war Daleks, (TV: Revelation of the Daleks) but eventually Dalek force field technology advanced to the point where bastic bullets were no longer effective against them, though the eyepiece remained susceptible. (TV: The Parting of the Ways)

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