Most of the 40's are nothing more than a modified 9mm.
Steyr and H&K are the only ones that aren't derived from a modified 9mm.
Beretta, Taurus, Smith & Wesson, Ruger, Glock, SIG-Saur, Browning HP, etc are based on the 9mm frame, magazine, & barrel outer dimentions.
Glock had to throat the chamber of the 40 in order for the bullet to feed correctly resulting in bulged brass at the 6 o'clock position due to the unsupported chamber.
The outer dimention of the Glock 40 barrel is the same as a 9mm, so why does the 40 have a thinner wall than the 9mm?
A: Because Glock wanted to be the 1st to get to market a .40 without having to do a redesign.
Why do you think 99% of all Kabooms are with Glock 40's?
Kabooms are rare, but when they do happen, usually the gun will be a .40 caliber Glock.
This is what a .40 chamber should look like, compare this to a Glock chamber.
Again, 99.9% of the Glock 40's are safe, 99.9% means that 1 in a thousand are not safe, so chances are in your favor if you happen to own a Glock 40.
Maybe it should be 99.99%, that would be 1 in 10,000
There are a lot of Glock 40's out there and this may be the reason we hear so much about the Glock 40 kabooming.