The LMG is similar to the gun used on the improvised turret. It fires a 6 round burst, and is notable for its high damage per second (DPS).
The LMG is typically equipped by raiders (bar tribals) in the mid-late game, but can also be purchased for a moderate price, or crafted at a machining table. It has the longest burst out of any standard weapon in the game (bar the minigun and heavy charge blaster), which is shot at a moderate rate. The primary downside to the LMG is its poor accuracy, which makes it fall behind the charge rifle in most scenarios in terms of overall damage output - but the LMG can pull ahead against larger foes, or indeed at higher quality levels, or in the hands of a shooter with a pair of bionic eyes and/or consciousness-boosting drugs such as Luciferium or Go-juice (the former further boosting sight).
If one is equipped with an excellent quality or better LMG and has bionic eyes and/or arms and on the aforementioned drugs, you'll have a very effective shooter in your hands. LMGs are well-supplemented by a few survival rifles as they can pick off enemies at longer range, or more accurately - while the LMGs shred those that are closer.