Vintage PPK recoil spring

Does anyone have any recommendations on the correct recoil spring to use for a 1965 dated Walther PPK in 380acp? Before ordering one I wanted to make sure a modern spring would actually work. I tried putting my S&W ppk recoil spring on the 65 and it will not work; the slide will not go back far enough to attach to the frame. Then after trying a recoil spring off an interarms version from the early 1990's almost the same exact thing! However, I was able to get the slide back far enough to attach to the frame, but taking back off again was nearly impossible! I am not sure why a newer spring doesn't work? Both springs off the S&W and Interarms versions are shorter than the original and don't appear to be any thicker. Thank you for your help!

From left to right is the original spring off the 65 (or at least what was in the gun when I acquired it) then the interarms spring in the middle and the S&W on the right.