in this case, the fired case ejected. The case was not split. I talked to Glock USA tech rep on the phone. He said it sounds like the broken spring caused the issue. I am going to replace the guide rod/spring. Is there a better aftermarket brand to get, or is the OEM piece adequate
This particular pistol was made in 1996. My brother in law carried it as an active duty Federal officer in his last posting. Part of his job was as a firearms instructor. I talked to the BIL today, and he says that pistol probably had over 5000 rounds through it. He subsequently gave it to my Son.
I'm glad that your son is OK.
It sounds like this was not a "kaboom" though. Kaboom, to me, means a catastrophic failure of some sort. And likely related to a design or QC issue with the firearm or ammunition.
The issue that your son experienced, sounds like a maintenance issue. The pistol has a spring-mass system, and the spring sounds like it was worn and perhaps the reason why he had two failures to fire. Some semi-autos will release the striker even if the slide is not 100% in battery. If it is too far out, it won't fire. But if it's in that in-between zone, some of the energy will go towards moving the slide forward instead of being directed towards the primer. You can confirm this with any semi-auto pistol, unloaded of course. See how far out of complete battery that it will release the striker.
Anyway, if the RSA was worn and resulted in what I speculated above for the failures to fire, but then the slide was 100% in battery for the next attempt, then there was no kaboom. The pistol just had a compromised spring, in the spring-mass system. There simply wasn't enough slide mass to compensate for the weakened spring.
I remember hearing claims of the Glock 21 having a reputation for kabooms, but I don't know if those were real either. And as far as I know, the early Glocks in 40 S&W had reputations for being unreliable, especially with WML, and long-term durability issues, but not kabooms per se.
