I received a standard 14 lb. replacement recoil spring from Wolfe for my 645. From other posts on this topic I figured it would be much longer than my current factory spring. No so -- they were nearly identical in length.

I went ahead and installed the new spring easily and stored the old one in the case for a spare.

Your original spring is probably ok. I just replaced my 645 spring with a Wolff 14# standard and it was 3/4" longer. My old one measured 6 3/8".
Vinny

If you look at the frequently asked questions section on the Wolff Gunsprings website, they address the question about lengths of new springs compared to the origionals. I have personally used Wolff products for several years on S&W and Colt pistols and have had no issues. They make a great product that is as good or better than the factory springs.