As Jill head immediately towrds the room that contains the shotgun after Barry speaks of investigating the mansion. Take the gun from the shelf and immediately run into the room with the collapsing ceiling. Try to open the door leading out. It will be locked and run back to the other door. Its now locked to. A cut scene will occur where Jill is screaming for help as Barry blasts the door and saves her. You get the shot gun there instead of having to progress without it. In tight situations you can now pack a little extra fire power.