There are three reasons given for Kbi.
The design of all Glocks have what is called unsupported chambers.
This is correct and not a 'myth'. A number of police agencies, including the New Mexico State Police, Bernalillo County Sherriffs along with the Georgia State Police and a host of others, are switching to the S&W MP. The previous experiences with KBi is due largely to case failure and overpressure.
The Glock does not fully support the entire case in either the 40, 10mm or the 45. In the case of the 40, this was to facilitate reliability in chambering, however, this left part of the case open to overpressure.
The argument on KBI comes from some blaming the gun for the failure, while Glock blames the ammo for it.
Since bullet seating is most important for the cartridge, and the ammo makers are not 'perfect' all the time, I believe there is a combination of both at fault.
Bullet seating on average is excellent, but there is that minor, albeit dangerous, occurence of a bullet seated too far or too 'loose' and can deep seat in the case as it hits the feeramp. This will cause a dangerous overpressure situation and KBi chance. This issue, combined with the steep feed ramp necessary for the 40+ cartridges in the Glock frames to feed reliably, are causing issues with KBi's.
The chances are greater in some of the older Glocks than the newer ones.
The Springfield XD is fully supported, however, they do not have the 'use and abuse' history that Glock has.
There are three reasons given for Kbi.
The design of all Glocks have what is called unsupported chambers.