It would be hard for a Glock 21 to kaboom. My understanding is that a Glock kaboom is a case split due to poor head support in high press rounds like 40 & 10. A 21 is a 45 ACP which runs at about 1/2 40 pressure.
The Kaboom is the case burst and usually the damage is cause by the gas jet cutting parts.
I'm not really in the know about kabooms though.