The venerable .45ACP has long been called "America's cartridge". Cool, right?
There you go, the main advantage of the .45ACP.
Hey, I'm a longtime .45ACP shooter. I still own 9 pistols chambered in .45ACP, and I only own 10 pistols
combined chambered in 9 & .40.
I carried a couple issued .45's on-duty over the years, but also carried issued 9's and .40's, and
more of them over the years since I carried an issued revolver.
I like my .45's. A lot. Always have.
I own a Blackhawk Convertible with .45ACP & .45Colt cylinders. (I prefer shooting it with the .45Colt cylinder, as the .45Colt has a
lot more potential for loadings, going back to my handloader days.) Shooting the Blackhawk with the ACP cylinder seems a little anticlimactic, by comparison.
The .45ACP's recoil is more of a slower push and mild muzzle whip, but it's more than many shooters care to shoot, especially trying to control it in rapid fire situations. Newtonian physics wins out in such things.
The pistols made for .45ACP can become a bit less tolerant of both shooter and ammunition influences the smaller they become, too. This can cause some frustration for some shooters when it leads to an increased potential for some types of functioning issues.
The older a .45ACP shooter may become, the more annoying or painful the .45's heavier (albeit slower dwell time) recoil may become, especially if repetitive stress injuries like "tennis elbow" may be involved, or even arthritis. It's not exactly uncommon for aging heavy caliber revolver and pistol shooters to discover they can shoot 9's more easily and with less aggravation and pain. I've heard my fair share of longtime .45ACP aficionados acknowledge they've changed over to shooting more 9's than their beloved .45's because of the reduced recoil and lessened pain.
Hey, some enthusiasts just like to look at the chunky fat .45ACP bullets and think they "look effective". (I kid you not.)
As far as the increased momentum of the mighty .45ACP slapping small steel plates or bowling pins off a table? Uh, walk up and gently slap one of them with the palm of your hand and watch them fly off the table even faster and farther. People may indeed
fall down for some gunshot wounds, but not because of "knock down power".
I like .45's, but I don't carry them quite as often anymore. Why? Because they're generally larger, thicker and heavier than my 9's, .40's or .38SPL's, and sometimes that matters to me as I go about my various activities.
Suit yourself.
Oh yeah, when the .45ACP became an option for the guys and gals to carry at my former agency, it was chosen by close to 70% of the people (the other option was initially, .40, and then 9mm was added back into the mix).
Once those guys and gals started having to shoot and qualify with the .45's, a line started forming of people wanting to trade the .45's for lighter recoiling and more easily controllable calibers. The demand for 9's started to increase ... even among some of the longtime instructor staff who were .45ACP enthusiasts and shooters. Why? Because the 9's were lighter and a bit thinner on the belt, easier and faster to control in shot strings and they could carry more rounds for the same number of magazines. As a piece of LE safety/work equipment (meaning duty weapon), the 9 has some nice attributes.