[Herb]

ESU, it sounds like the bolt is binding somewhere in the rails. Try disassembling it, then use a black 'magic marker' to cover the worn areas (where the blueing is gone) and then cycle the bolt several times. Take it apart again and see if there are areas where the marker is rubbed off. If there are some areas that would be where the binding is occurring. Try using a fine sand paper on the high spots, about a 400 grit, do it again and see what the results are. You may have to do this several times to get it leveled out, don't get in a hurry, if you over do it, big problem with the fit. Before doing the sanding try to determine if the bolt is the culprit or if the slide rails are causing it. You might try cleaning and blacking the entire bolt assembly on the first attempt, that should give you a good idea if there is a binding problem somewhere.