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My strain screw is right at 15mm (about 9/16") long. I once got a Model 15 that had the mainspring bent in the middle, I don't really know what the point was. I replaced it with a Wolff spring before I ever shot it.

I just checked my Model 19 with the same grips, and it appears that the mainspring in your picture is much too straight. I strongly suspect that someone cut down the strain screw to get a lighter trigger pull. Make sure yours is tight, and, if so, you'll probably need a new screw.