Mainspring Question

[MarkC]

I have a "shooter" Luger that I posted some pictures of in another thread that apparently is a parts gun made from an old Erfurt frame. The mainspring may be a little soft since it jams a shell casing on occasion.

Any tips on replacing the mainspring? I hear they can be a problem to put back in. Are there any tools that you would recommend to compress the spring?

Thanks!