I’ve never understood the recoil of the 40s being so much worse than the 9mm such that it made whole departments switch.
But I continue to hear that …. story?
The problem with 40 isn’t as much being hard on shokters but it’s hard in guns. 40 is better designed for and ran through either steel or alloy frame guns OR they run a handgun actually designed around the 40 (HK USP, Sig 229, S&W M&P) vs an existing 9mm and just throwing a 40 cal Barrel and breech plug in (Glock Beretta 92/96 etc)
And with the not followed firearms maintenance by most departments they were having to replace broken guns way more frequently. One reason Glock went to the 2 spring guid rod system agencies (and users) nebwr changed the springs as frequently as recommended
And an example of that is on Glocks Gen 5 40 cals have a wider and slightly heavier frame than the Gen 2-4 40 cals
The other thing that kept 40 in popularity was it was the limited caliber of USPSA whem they had 2 divisions up until around 2004 when they started expanding and one could compete with a 9mm in production class
There is also a cost factor for large agencies especially since Covid.
From my time associated through FLETC Feds carry duty ammo from three main places Hornady 135 plus p Critical Duty, 124 plus P and 147 Gold Dot and 124 or 147 HST and they are killing a lot of folks with them
Even the Border Patrol running 147 G2 Gold Dot while some amature gel testers call it a failure with their one round shoddy test it’s funny that is the duty load for Border Patrol, LASO and DEV Group (aka Seal Team 6) and people are getting shot almost daily with it and dying