Sure you can take the assembly apart. That's how you change the shot and powder bushings. You HAVE changed the shot and powder bushing before haven't you?
As Tom said, just remove the screw on the side, turn off the shot and powder shutoffs, and lift the assembly out and up off the frame. Tilt the powder and shot tubes and pour the shot and powder into separate containers. Then remove the charge bar out the rear of the housing. The measure plate will fall out at the same time. Check for any obstructions and then reassemble. My guess is that something has become wedged in there and that is limiting the travel of the charge bar. I've never had that happen to me in the many thousands of round of reloading I've done, but I guess it's possible that it could happen. When reassembling, be sure to get the powder shutoff slide spring in there properly or it can cause the slide to bind. It's actually much simpler than what the written description sounds like. Good luck and let us know how it goes.