The Q-System shoots two bullets at once at the cost of only one ammo, unlike other Atlas assault rifles that generally shoot only one bullet at a time. For this reason, it always comes with the "Cost-Effective" prefix.
Like other Atlas weapons, it comes with an Alternative Fire mode that shoots a tracker puck, grenade or dart. After an enemy is hit, the primary fire mode's bullets will home in on that target for a set duration which is stated on the item card.
The Q-System is obtained randomly from any suitable loot source.