Firearm

Firearm, commonly known as a "gun" was a term encompassing a variety of weapons which used a projectile fired from the weapon relying on chemical explosives to propel the projectile at high velocities from the firearm. They were typically used to penetrate surfaces to maim or kill and were usually human in origin.

Most firearms were ineffective against armored races such as Daleks and Cybermen, (DW: Army of Ghosts/Doomsday) though specifically designed bullets were produced to take advantage of alien races' weaknesses (Gold in the Cybermen's case). (DW: Battlefield) Standard bullets were effective though against biological species similar to humans, such as the Ood, (DW: Planet of the Ood) and Sontarans. (DW: The Poison Sky)

Firearms, as a relatively primitive technology, could be neutralized by more advanced technology. For example, Sontaran soldiers employed a cordolaine field that affects certain metals such as copper, causing weapons using copper casings on their projectiles not to fire. (DW: The Sontaran Stratagem/The Poison Sky)

Technological improvements such as the Bastic bullet could make firearms more effective, a viable weapon even against a Dalek. (DW: Revelation of the Daleks, The Parting of the Ways)

One practical limit on the use of firearms is that they were usually lethal. While it was possible to use a firearm to incapacitate rather than kill, this could be done only by inflicting serious injury and pain. While there were forms of ammunition known as "less than lethal" intended for incapacitation, such as rubber bullets, they still inflicted great pain, and were lethal under certain circumstances. For this reason, individuals such as the Doctor and Sarah Jane Smith refused to use them on moral grounds. (DW: The Stolen Earth/Journey's End)

Despite their limitations, humans were known to use firearms well into the 2001st century and beyond. (DW: The Parting of the Ways, Utopia)

An appreciation of the usefulness of firearms was not limited to humanity. Upon landing on the planet Exxilon a Dalek taskforce's weapons were rendered inoperable, forcing them to replace their energy weapons with semi-automatic ballistic weapons. (DW: Death to the Daleks)

Bolt-Action Rifle use

 * John Andrews used a Lee-Enfield when he chased the Third Doctor and Jo around the deck; it was a result of Vorg having changed the specimens' personality to violence. (DW: Carnival of Monsters).

Assault Rifle use

 * Weapons resembling M4 Carbines with Beta C-mag drum magazines were used to shoot and subdue the Ood on the Ood Sphere. (DW: Planet of the Ood)
 * The army and UNIT used H&K G36 assault rifles against the Sontarans, Daleks and the Cybermen. They were completely ineffective against the last two. (DW: Army of Ghosts/Doomsday, The Poison Sky, The Stolen Earth/Journey's End)
 * Gwen Cooper and Ianto Jones used assault rifles to combat a Dalek in the Torchwood Hub. (DW: The Stolen Earth)
 * The Master's private armed teams fired on the Tenth Doctor, Martha Jones and Jack Harkness with assault rifles. (DW: The Sound of Drums)
 * Captain Jack led a squad of men to shoot the Toclafane with assault rifles. He also destroyed the Paradox Machine by shooting it with one. (DW: Last of the Time Lords)
 * The Preachers used a number of automatic weapons to fight the Cybermen, notably the Kalashnikov AK-47 assault rifle. (DW: Rise of the Cybermen)
 * Miss Foster's guards were armed with assault rifles. (DW: Partners in Crime)
 * The security guards in the International Gallery and the police units waiting to arrest Christina de Souza at the end of the tunnel were armed with Heckler &amp; Koch G36 assault rifles. (DW: Planet of the Dead)
 * UNIT successfully battled three of the Swarm with Heckler &amp; Koch G36 assault rifles and M4 carbines, although anti-aircraft batteries served a key role in finishing the creatures off. (DW: Planet of the Dead)
 * Joshua Naismith's private guards were armed with M4 Carbine Assault Rifles, which they employed to put suppressing fire on the Tenth Doctor. (DW: The End of Time)
 * British Army soldiers were seen armed with L85 assault rifles at the Albion Hospital and in Downing Street. (DW: Aliens of London/World War Three) In all other appearances, British Soldiers were armed with G36s.
 * US Air Force personnel guarding the Eleventh Doctor at Area 51 were armed with GAU-5A/A Assault Rifles. (DW:Day of the Moon)

Handgun use

 * Two fake police were in possesion of handguns equipped with silencers. (DW: Attack of the Cybermen)
 * Gustave Lytton gave a handgun to Payne. The Sixth Doctor took it after his death and Russell took it when he arrested the Doctor. (DW: Attack of the Cybermen)
 * Brigadier Lethbridge-Stewart and members of UNIT threatened the Master with handguns. (DW: The Claws of Axos)
 * The Lorduke of Zazz threatened Frobisher with a handgun. (DWM: The Gift)
 * When the lone Dalek escaped The Vault, the security guards used pistols against it, to no effect. (DW: Dalek)
 * Jo Grant brandished a revolver when tracing the Master to Devil's End. (DW: The Dæmons)
 * When Suki Macrae Cantrell was promoted to Floor 500, she pulled a modified Smith & Wesson Model 669 pistol on the Editor. She fired the pistol at the Jagrafess, to no effect. (DW: The Long Game)
 * Jack Harkness used a 21st century era pistol against the Daleks invading the Game Station, probably a Beretta 92FS. (DW: The Parting of the Ways)
 * Queen Victoria carried a small Webley Bulldog revolver in her bag for her protection. She shot Father Angelo with it. (DW: Tooth and Claw)
 * Maximillian Stael commited suicide with a handgun given to him by the Fourth Doctor at his behest. He did this to avert the Fendahl from using him as a power source. (DW: Image of the Fendahl)
 * Jake Simmonds and Mrs. Moore pulled pistols (a SIG-Sauer P226 and a Beretta 92FS) on Mickey Smith when they found out he wasn't Ricky Smith. (DW: Rise of the Cybermen)
 * Tallulah had a prop Webley Mk VI to scare the Tenth Doctor, Martha Jones and Solomon. (DW: Daleks in Manhattan)
 * The Master's henchmen pulled out pistols (Glock 17s) to everyone witnessing when the Toclafane killed President Winters. (DW: The Sound of Drums)
 * Thomas Milligan used a Heckler & Koch USP to lure a Toclafane to the trap set up by Alison Docherty. Lucy Saxon used a Glock 17 to kill the Master. (DW: Last of the Time Lords)
 * Jack Harkness carried a Webley Mark IV revolver while in service with Torchwood, despite the rest of his team carrying more modern semi-automatics. The Webley Mark IV in .38 calibre, rather than the more famous .455, was a British Army sidearm during World War II and afterwards. (TW: Everything Changes)
 * General Cobb intended to shoot the Tenth Doctor with a Webley Mk VI but Jenny got in the way. The Doctor later almost shot Cobb as revenge for killing his daughter. (DW: The Doctor's Daughter)
 * Colonel Mace shot Commander Skorr with a SIG P226. (DW: The Poison Sky)
 * General Sanchez attempted to repel the invading Dalek with a stainless Ruger GP100. (DW: The Stolen Earth)
 * John Jefferson shot an Ood with a Glock 17. He only fired one shot. Probably the magazine hadn't been loaded properly, or the gun jammed. (DW: The Satan Pit)
 * The Fourth Doctor took Scorby's handgun and used it to retreat in safety. He told Sarah he'd never use it but they didn't know that. (DW: The Seeds of Doom)
 * Captain Erisa Magambo threatened Malcolm Taylor with a Walther P99 pistol, and later used it to defend against three of the Swarm. (DW: Planet of the Dead)
 * Wilfred Mott took his old Webley Mk IV service revolver with him when he sought out the Tenth Doctor. He later gave it to the Doctor, who took it to use against the Master. The Doctor had to choose between shooting the Master or Rassilon, but finally chose to shoot the nuclear bolt, destroying it and breaking the link that anchored the Time Lords in the present time, sending them back into the Time War and saving the universe. (DW: The End of Time)
 * The Fifth Doctor used a handgun against a Dalek mutant that had escaped from its damaged armour. He decided that he needed to kill Davros but when the moment came he couldn't bring himself to pull the trigger. (DW: Resurrection of the Daleks)
 * The Sixth Doctor used an automatic pistol against a Dalek's eye stalk. (DW: Revelation of the Daleks)
 * The Eleventh Doctor fired a handgun (possibly a SIG-Sauer P225) to destroy a Gravity globe. (DW: The Time of Angels/Flesh and Stone)
 * Amy Pond used Canton Delaware's handgun on a little girl in an astronaut suit, not knowing she was her daughter Melody, in an attempt to save the Eleventh Doctor. (DW: The Impossible Astronaut, Let's Kill Hitler)

Machine gun, Submachine gun and PDW use

 * Inside the Miniscope, the crew of the SS Bernice used submachine guns against the Drashigs to no avail. (DW: Carnival of Monsters)
 * Gustave Lytton had a silenced submachine gun. (DW: Attack of the Cybermen)
 * Mounted machine guns were used to shoot the Scarecrow Drones when they attacked the Farringham School for Boys. They trained with these in the school grounds. (DW: The Family of Blood)
 * Harrison Chase's guards all carried submachine guns. (DW: The Seeds of Doom)
 * The crew of a Delta III refinery had two machine guns. (DW: The Power of Kroll)
 * On Malcassairo, the guards repelled the Futurekind with machine guns. (DW: Utopia)
 * During the Hath-human war on Messaline, the humans used a weapon resembling an FN P90. (DW: The Doctor's Daughter)

Behind the scenes

 * Most firearms used in the 2005 series, are of Heckler &amp; Koch manufacture, specificaly G36 assault rifles and USP sidearms. Glocks and Webleys have also been used.
 * The guns carried by Sanctuary Base 6 security in DW: The Impossible Planet / The Satan Pit are P90 Personal Defense Weapons fitted with suppressors (the same model of weapon commonly associated with Stargate SG-1 universe).
 * In the various UNIT episodes during the Jon Pertwee era, Sterling sub-machine guns or SLRs were used.