The 40 story is interesting.
Smith and Wesson is to be commended for it.
In days of old when 10mm was the big thing and the FBI were shooting it and they discovered there men could not shoot it well ( similar to another tragic story and the CHP with 357 Mag). Several men (Officers) died because of the over power of the bullet and so it was with the Newhall shooting in the CHP.
FBI came up with the FBI 10 mm, it was 10mm with less power. Smith and Wesson realized the casings were full of air and decided to make the 40 S&W to the FBI 10mm specs, shorter cartridge (case)/ bullet over all, and not quite as bulky of a gun.
The reason the FBI went with special ammo was they had bought a large amount of guns to shoot the 10mm and didn't have the budget for another gun and round, so they had a company make up the FBI special 10mm. Pretty much what the 40 S&W is today.
So they had a 10mm in hot loads and a 10 mm in lighter loads. Sort of like the 38 and 357 but the case was the same in all of the 10mm's.
That is the basic story give or take a few words. It is a good round and a smaller and lighter gun.
Many of you don't like the snap? Come on, you can always add some weight in the magazine remover well, of the Glock and it will help. They make one in brass or lead. I think??? You can fill the mag full and only shoot the first 3 and reload till you grow up to the load.
So that is the story as close as I can recall, off the top of my head
HQ