About 15-18 years ago the local sheriffs department had MP5's chambered in 40 S&W. They used the local conservation area shooting range and I was normally able to pick up all of their brass. Needless to say I have plenty of 40 brass to last me quite a while.
But as others have stated. Everyone jumped on the 40 S&W band wagon when the FBI started using it. And when the FBI went back to 9mm then a lot of police department and civilians went back to 9mm also.
I personally like 40 S&W. Yes it definitely has a different recoil impulse compared to 9mm in the same sized pistols but the recoil is still not bad. I even bust out the Hi Point 4095 Carbine in 40 S&W now and then just for giggles. That thing is very accurate for being so cheap ($179 when I bought it)
You should give one of these conversions-
https://www.hightowerarmory.com/High-Tower-Armory-MBS-95-40-SW_p_48.html
This isn't a typical cheap, POS stock replacement. I'm a retired SWAT commander, and a master armorer/gunsmith. I've been doing this type of thing for over 30 years, to say I'm difficult to impress would be an understatement. The hi point carbine is robust and dependable, and that's about all I can say about it that's positive... It is accurate, once you add decent sights.
The high tower armory bullpup system for the little carbine is amazing. (I'm not affiliated with them in any way, just a fan) the only downside is the trigger. The original trigger is a POS and the conversion doesn't change that. If you use your imagination, while you have it apart, you can improve it- just think of ways to reduce contact or smooth areas where contact is unavoidable.
I'm not saying I'd trade my MP5 for a high tower armory PCC, but if you own a hi point carbine, this conversion makes the little carbine more enjoyable and more lethal, if the situation called for it.
As for the .40-9mm debate... Like most men my age, esp military folks, we were raised on the 1911. .45 acp was the favored man killer round for handguns.
Political correctness in the police department meant saying goodbye to "cocked and locked". I got dozens of phone calls per week complaining that our damned fool officers were running around with their guns cocked! *Sigh*
So about that time the new plastic Glock came on our radar. I hated the idea. So the chief deputy sent me to Smyrna Georgia to Glock armorers, advanced armorer, and Glock tactical schools. I came back a changed man.
That experience deserves its own book.
So we adopted the G22 for uniforms, the G23 for detectives, plain clothes etc, and the G27 for backup, off duty, undercover work. The .40 was our caliber of choice because the Speer Gold Dot ammo performed very close to .45 acp ballistics while capacity remained high like 9mm. Additionally, an FBI shootout down near San Antonio resulted in two dead agents, because their anemic 9mm pistols wouldn't penetrate the windshield. This is Texas, we found those boys and killed em back, but that didn't help those agents. RIP fellas.
So no 9mm for us. We never regretted it, both the Glock and the .40 served us well for decades.
I had been a fighter pilot as a young man, flying the mighty Eagle, F-15C, for the United States Air Force. When I left the service aviation was in a slump, so I ended up in law enforcement. I flew a Lear jet for a company on my days off. But aviation saw a massive resurgence, so I kissed my badge goodbye and flew around the world for awhile before settling at Continental airlines. I spent 22 glorious years there, after retirement I returned to law enforcement, eventually commanding 3 narcotics entry teams. (SWAT)
To my surprise, we were back to the 9mm!
First thing I did was buy a bunch of ballistic gelatine to make targets, to test the standing belief that ammo had improved so much that larger calibers were no longer needed.
After shooting all day at various targets through various media I came to two conclusions:
1. Ammo had improved dramatically. 9mm was much better than it had been.
2. The same thing was true for .40 ammo. So we switched back to .40
When asked why, I just repeated that old law enforcement gag:
"Officer, why in the world do you carry a .45 caliber handgun??"
" We'll ma'am, mostly it's because they don't make a .46."
True enough.