The 40 is just a detuned 10mm. The FBI not happy with the 9 wanted the 10. At the time the guns of the era couldn't handle the pressures so a little detuning and you have a 40. It was also not fun for small statured and female agents.
Now days I believe the 10mm is coming back, the 40 seems on the way out. All the agencies in our area are now going back to the 9mm. More capacity. Kind of a large circle. Took me 15 years to get 45's in our officers holsters after starting with 9, then 40. Ours are still issued 45's but if they desire they can purchase a 9. Part of that is the sudden urge for red dot sights which can easily be installed on the 9 Glocks but not the 45's yet, that and holsters are always behind on the real caliber guns for some reason.
I like the 40 in a full size gun although I don't have one and probably won't get one. I have a K40 but it's a safe queen and will likely stay that way.
In Memory of Paul "Dietrich" Stines.
Dad: Say something nice to your cousin Shirley
Dietrich: For a fat girl you sure don't sweat much.
Cue sound of Head slap.
RIP Muggsy & TMan
"If you are a warrior legally authorized to carry a weapon and you step outside without that weapon, then you become a sheep, pretending that JOCKO will not come today."