I am not a glock expert by any means, and I do not want to insult the OP, but at first glance my first thought was that the face plate of the spring assembly is supposed to be set down all the way into the half moon notch of the barrel. I believe half moon is the term the glock manual even uses. It would seem to me that if the spring jumped out of the notch when the slide was assembled then when you fired this is what would happen. I know the first time I reassembled my glock I did not have the spring all the way into the notch. I was being extra cautious though because it was my first time so I removed and redid the spring until I wa sure I had it right.
This is from the "unofficial" manual on the internet:
"Reassembly Note:
When installing the recoil spring tube and recoil spring, be sure that the back end of the recoil spring tube rests
in the half moon cut in the bottom of the front barrel lug. If it is not properly seated and you reassemble the
pistol, the recoil spring tube may be damaged."