Which weapon is commonly used as a machine gun and fires from an open bolt?

The M249 SAW (Squad Automatic Weapon) is recognized for its design as a light machine gun and operates using an open bolt mechanism. This mechanism allows the weapon to cool more effectively when not being fired, as the bolt remains in the open position, enabling faster cycling and reducing the chance of overheating during sustained fire.

In addition to its role as a machine gun, the M249 is known for its ability to be fed from both linked ammunition and magazine, making it versatile for various combat situations. The open bolt design also contributes to a low rate of fire, which can help improve accuracy during automatic fire.

Contrastingly, while the M4 is a carbine known for its versatility in personal defense and close-quarters combat, it operates from a closed bolt, which provides better accuracy for semi-automatic fire. The 240B is a medium machine gun that also uses a closed bolt design, while the Makarov is a semi-automatic pistol and does not function as a machine gun at all. This makes C the clear choice for this question regarding a weapon that is commonly used as a machine gun and fires from an open bolt.