I just received my first Graphic camera... a Crown Graphic 23. I know its technically a medium format camera, but I'm posting it here because (a) it has more in common with LF cameras than most MF and (b) I figure all the 4x5 Graphic people hang out here. Anyway, The camera came with a "23" Graphic 6x9 roll film back (knob wind). When I remove the ground glass, and secure the roll back, it seems to seat properly, but there is nothing stopping the entire back from sliding off the camera to the right. There is enough friction that it doesn't just fall off, but a nudge will push it pretty easily, potentially exposing my roll. Am I missing something here? It is a graflok back, btw.