If I understand correctly, it is stiff or difficult to swing the cylinder out when pressing the cylinder release? Two possibilities, one is the forward side plate screw (which holds the crane assembly in) has been mixed up with the middle one. The forward one in many cases has been dressed down to properly allow the crane freedom to swing down. The other possibility is being a 1948 gun, has the cylinder assembly , crane, ever been removed for cleaning? If not, the original lubricant could be all gummed up and just needs to be cleaned up and a drop of light oil applied.
1st, make sure you have a proper hollow-ground correctly sized screwdriver, then try loosening up the forward side-plate screw, just about a half turn, and see if that helps. If so remove both front and middle side plate screws and see if the middle one is shorter, if so it is the front screw. If that doesn't help, remove the front side plate screw and gently swing out the cylinder and work the crane out of the frame to check on the lube.
If neither of these help, you may have a an ejector rod that has backed out. It has a right hand thread. Needs to be tightened, (but don't put pliers on it without a piece of leather to protect it.
