It's the recoil spring. You need a new one, or you might get away with turning
it around so the buggered part is on the rod.
Pasted from my other reply:
HD Military---If you want to remove the slide it's a little tricky.
Pull the slide back, then depress the little button on top and let
the slide forward. At that point there should be no recoil spring
tension pushing the slide forward. Then rotate the little lever on
the side forward and slide the slide off of the frame. If you don't
use the little button to lock the recoil spring back, you will trash the spring.