Firearm

The Machine gun was a weapon created on Earth. The weapon fires projectiles (bullets) at a high, automatic rate. They are more widely available than Pistols.

This type of weapon was generaly inneffective against such alien races including the Daleks and the Cybermen, but are effective to kill Ood and pierce Sontaran armour, if the bullets weren't influenced by the cordolaine. Machines were still widely used by the people of Earth beyond the 21st century.

Appearances

They were used to shoot and subdue the Ood both on Sanctuary Base 6 and on the Ood Sphere. (DW: The Satan Pit, Planet of the Ood)
The army and UNIT used them to repel the Sontarans, Daleks and the Cybermen. (DW: Dalek, The Parting of the Ways, Army of Ghosts, Doomsday, The Poison Sky, The Stolen Earth, Journey's End)
Gwen Cooper and Ianto Jones used machine guns to combat a Dalek in the Torchwood Hub. (DW: The Stolen Earth)
The Hath and Humans on Messaline carried heavy duty blaster rifles which were used to fight the war over who took control of the planet. (DW: The Doctor's Daughter)
The Master's private armed teams fired on the Doctor, Martha Jones and Jack Harkness with machine guns. (DW: The Sound of Drums)
Captain Jack led a squad of men to shoot the Toclafane with machine guns. 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. (DW: Rise of the Cybermen)
Mounted machine guns were used to shoot the Scarecrow Drones when they attacked the Farringham School for Boys. (DW: The Family of Blood)
On Malcassairo the guards repelled the Futurekind with machine guns. (DW: Utopia)
Miss Foster's guards were armed with machine guns. (DW: Partners in Crime)

Behind the scenes

Most machine guns used in the series were Heckler & Koch G36s.