locking back the slide won't do anything even if it was locked back for 20 yrs. Compressing a spring does not cause a spring to loosen. Only cycling a spring will do that. That's why you can leave magazines fully loaded for years (rust free) and they will function just fine. Compression causing a spring to lose its "spring" is a myth.You can also leave the slide locked back a couple of nights at a time to help loosen up the spring. Maybe go with some blazer brass 124gr, that's fairly cheap to get if you shop around online.
Good luck <img src="http://www.waltherforums.com/forum/images/smilies/smile.gif" border="0" alt="" title="Smile" class="inlineimg" />