They're blasted out the barrel, that shit is not going back at your face in any meaningful amount. That would be the worse design ever if hot gases came back into the face of the operator. The only real danger about aerosolized lead is if you're running a suppressor and in an indoor range with shit ventilation, and those are usually shut down pretty quickly. The fire Marshal will shut that shit down in a heartbeat if the ventilation is shit (unspent gunpowder is stupid flammable).