After getting Prothean squad member, I unlocked Prothean assault rifle. I wondering, since it has unique mehanics, how ammo power (in my case, incinerate ammo) is triggered while using this weapon?
Each time a weapon does damage, it has a chance to trigger the ammo power. Chance varies based on weapon type (otherwise a shotgun shot spread of 3, 6, or 8 pellets would more often than not trigger the power)
The Prothean Rifle triggering ammo powers is no different than the Scorpion (exploding pistol), Arc Pistol (energy pistol), or Geth Plasma Shotgun (energy ball shotgun) triggering them - inexplicable, but useful.