A mini-gun with 6 rotating barrels fires 6,000 rds a minute, 100 rds a second, 1500 rds in 15 seconds. If you have a vehicle to mount it on and to carry the ammo.
Military version Model-162 Rifle?
Caliber 5.56 mm
Automatic 700–950 rounds/min
Sustained Semi-auto? 45-60 rounds/min, 1 per second or the barrel melts and rounds explode in the chamber.
Realistically? 15 rounds in 15 seconds.