With today's defensive ammo 9, 40 and 45 pretty much all have similar enough results that I'll take the additional ammo of the 9mm. There are simply times when you'll need more ammo then something that hits slightly harder and makes a 1/8" larger hole. I had originally decided on 9mm as my carry choice due to its price, weight, recoil, mag sizes and pretty much matching ballistics to that of the 40 and 45. After reading about Sergeant Timothy Gramins my choice was cemented.
For those who haven't heard of what happened... Gramins was in pursuit of a suspect who stopped, jumped out of his car and immediately started shooting at Gramins in his car. He drew his Glock 21 handgun chambered in .45acp and quickly got out. They circled his car firing at each other. In
less then 60 seconds Gramins had been fired at 21 times from 2 handguns and fired 33 rounds back at his attacker.
Here is the kicker..
Gramins HIT his attacker 14 times, 6 of those rounds struck vital organs and yet the guy never went down and continued his attack! The attack continued until 3 consecutive head shots were made to the attacker when he looked under the car. He had taken vital shot in his
heart, right lung, left lung, liver, diaphragm, and right kidney but continued attacking without slowing down until the head shots. His vital signs were still present even when EMS showed up where both were transported to ER where Gramins heard one doctor exclaim, “We may as well stop. Every bag of blood we give him ends up on the floor. This guy’s like Swiss cheese. Why’d that cop have to shoot him so many times!”
NO drugs or alcohol were found in the attackers system!
Gramins now carries a crud load on 9mm while on duty.
The complete account can be read here and is worth reading!
https://www.policeone.com/police-heroes/articles/6199620-Why-one-cop-carries-145-rounds-of-ammo-on-the-job/I'm not saying one handgun caliber is better then another since ballistics between the top 3 (9, 40 & 45) are close enough. Since ballistics are so close however, I'll take my 17rd double stack 9mm mags in my Classic Walther PPQ over a 7 or 8 round .45 1911 (which I own and love shooting) or the slightly heavier but more costly 40S&W (which I'll never buy into) simply to carry more rounds. Sure double stack 45s are available but they are also bulkier, heavier and more expensive to buy (usually) and to shoot. I spend a lot of time in schools and other populated indoor "soft" areas which are the more popular areas for shooters. I don't ever expect to be in a situation but then neither did any of those who have been! I don't carry umpteen mags on me but if god forbid something were to take place I'd like to have more then 8rd mags on me. A single spare mag gives me 35rds on my body, well concealed and doesn't weigh me down. Toss in a 2nd mag for 52rds that's still concealable, though not quite as comfortable, for those days