Machine Gun

Machine Guns are high caliber automatic weapons, that appear in Tomb Raider.

Tomb Raider Legend
Lara Croft can hi-jack Machine gun Turrets that were placed by James Rutland mercenaries.

They can tear through cover and have unlimited ammo.

Lara Croft and the Guardian of Light
Lara can unlock an M134 Minigun, known in game as the "Chaingun." Has high power and fate of fire, and medium ammo consumption.

It is one of the most powerful weapons in the game,

Tomb Raider
After collecting all Rifle Parts, Lara's Guerrilla Rifle will be upgraded to the Commando Rifle Which despite it's name is a Light Machine Gun. It is based of the Ultimax 100.

It can be upgraded, and all previously crafted upgrades carry over to the Commando Rifle. and it has several unique upgrades of it's own.

Multiplayer
A Type 1 Machine Gun appears in Multiplayer, both the a survivor weapon, and the turret. As a turret it has unlimited ammo, and can kill enemies in just a few hits, however sustained fire will cause it too overheat, and using it leaves the player stationary and vulnerable to enemies.

A Mini-gun also appears as one of the "Super Weapons" in Multiplayer. It offers massive Damage and Boasts a a 500 round Magazine, though it cannot be reloaded, and it useless once ammunition is gone. It must be retrieved from one of the designated spawn points.

Trivia

 * In Tomb Raider, when Lara returns to the beach after the realization that the Himiko's soul is the cause of the storms, in the alpha version of the game, Lara and Joslin Reyes had to fend off Solarii Brotherhood using the PT boat's machine guns.