Machine guns, also known as Light Machine Gun or LMG, are usually operated electrically.
The advantages of the LMGs are obvious: high capacity magazine and fully automatic firing mode. Some models are also equipped with a spring-quick change system which enables to increase the performance or they have an adjustable rate of fire (eg. the A&K M60).
It is advisable to have a pistol or small machine gun on hand for close range shooting (M11, MP5K, etc.).