The RPD is the FND's standard light machine gun, with a decent fire rate but few mod slots. Its Libertad Custom and Hammer Of The Gods versions fix that weakness.
It does the job of an LMG, but with so few mod slots it falls behind almost every other light machine gun. Use it until you find something better, or get one of its improved versions.
Sink Or Swim adds faster movement while aiming and better suppressor cooling, but like other uniques it cannot be changed at a workbench. Hammer Of The Gods and the Libertad Custom share stats and extra slots; only the skin differs.
It takes standard, armor-piercing, soft-target, poison, blast and incendiary rounds. You carry 200 rounds, or 500 with the LMG pocket.
BP-SMG
The BP-SMG is a compact submachine gun that sprays quickly from a 30-round magazine. It is a good close-range stealth gun with a suppressor, and its unique Iron Curtain fires soft-target rounds.
BZ19
The BZ19 is a submachine gun with a huge helical magazine of 64 rounds. You can hold the trigger far longer than with any other SMG, and its unique Turn Of The Century sits at Resplandor Agriculture in Lozanía.
M12
The M12 is a Beretta submachine gun with a 32-round magazine and three fire modes. Its unique Five-Alarm version comes from an insurgency, and São Paulo Stinger is a customizable variant.
M249 SAW
The M249 is a light machine gun, labeled Tacticool in game, with one of the highest fire rates you can get. It is sold only through Lola's Black Market or the online store.