A Sept. 22 pretrial conference has been set for two University of Massachusetts Lowell students charged with firing BB guns from their dormitory window, leaving a fellow student with minor injuries to her face and leg. The men, 21-year-old Sean Marchand of Deering, N.H., and 20-year-old Patrick Bogonis of Woburn, were ordered to leave their dorm pending the outcome of legal proceedings surrounding the incident, which occurred during the spring. Police responded to a report that a female student had been hit by a BB pellet while she and a group of friends were using a hula hoop outside. They were able to identify the dorm window the pellet came from. When police followed up, they found Marchand, Bogonis, and two air pistols.