Primary Weapons are main weapons used by soldiers. They vary in use and appearance. They are used along with Secondary Weapons. Each class can use 2 types of Primary Weapons.
Assault Rifles are balanced weapons with multiple uses. They can be used at the very start in the game. They aren't outstanding in any particular field, but some of them have really big firepower. They can be full-auto, semi-auto and burst fire. They are used by Engineers and Medics.
Duals are double weapons that alone could be better as secondaries, but together have great firepower. They vary use, as they can be pistols, SMGs, machine pistols and shotguns. They can be used by Gunslingers and Ninjas.
MGs are weapons with very fast fire rate, good damage and lots of ammo (some of them even don't have reloads). However, they also have low accuracy and mid range, so their firepower is effective only in close combat. They can be used by Mercenaries and Medics
Snipers are long rifles. They have the best accuracy in the game, some even perfect. They also have the longest range. However, Their fire rate is the slowest. Snipers are used for long range combat only. They are the best weapons to score headshots. They can be used by Gunslingers and Snipers
Shotguns are close range, inaccurate weapons that spread multiple bullets at once. They usually have high damage and they are the most powerful weapons in close combat. They can be used by Ninjas and Juggernauts.