If it ain't broke don't fix it! Having said that, sometime back, I had an old 40X that I had rebarreled that did not shoot as good as it should have. After eliminating about all the variables I could think of I happen to notice that there appeared to be a slight variation in the way the primers were being struck. I never did have a misfire. Replaced the spring and all was well! You can get a spring from Brownell (Wolf or Rem.) For what it's worth XP-Mod.7 springs are not available. I've had to use regular short springs and shorten them up.