[Herb]

I had a Luger that did the same thing, really hard to operate the toggles. I took it apart and 'miked' the reciever rails at thier rear most area. The correct measurement should be 13mm between the rails at that point, mine was 11mm!
How it got that way is a mystery to me, what I did was to take several of those wooden wedges that are used to shim doors or windows and drove them between the frame rails till they opened up to around 16-17mm and let it set for a day then drove them in even further and let it set again. After doing this several times and frequently checking the measurement I finally got them to 13mm at which point it worked fine. Check out the rail measurement on yours to see if it is actually 13mm, if smaller you might try what I did, if that bothers you then a visit to a gunsmith might be in order. I would not advise using a heat source to speed up this process, you might really mess up the original hardening of the metal.