A dead stop type projection window assembly includes a free-standing frame and at least one independent insert window. The free-standing frame includes a top member, a base member spaced below the top member, at least two mullions vertically extending between the top member and the base member and spaced apart to form an insert window opening therebetween, and a stop extending along a perimeter of the insert window opening. The insert window is secured to the free-standing frame at the insert window opening. The free-standing frame further includes at least one preformed seal member engaging the insert window to seal closed the window frame opening with a wind/water tight seal. The preformed gasket can extend from the stop to the insert window and/or can extend from at least one of the mullions to the insert window.