The best pistol caliber has been endlessly debated on gun forums and by gun enthusiasts alike. Everyone differs in their opinion, there is no concrete answer as to why one pistol caliber would supersede the other. The truth is, there's really no one-size-fits-all answer and it all depends.
I got across a really cool article from GunPros.com where they put comparison of different pistol calibers in simple terms. So what would be your next pistol caliber - 9mm, 40S&W, or 45 ACP? Let's take a look at some popular choices as defined by Gun Pros.
9mm 9mm is, in my opinion, the best pistol caliber for most people's needs. Many would consider it the smallest handgun caliber that you can be certain has enough stopping power for concealed carry and home defense. Some prefer .40 S&W or .45 ACP for these purposes, but 9mm offers less recoil, likely better accuracy, and allows for larger magazine capacity. These reasons are enough for the FBI and the majority of United States police officers to justify using 9mm pistols. Most of the United States armed forces are also issued 9mm pistols.
While it might seem a bit loud and surprising for some first time shooters (compared to say .22 LR), I think the vast majority of shooters should easily be able to handle its noise and recoil, so long as they're in reasonable physical shape. There are obviously some exceptions to this. For example, my mother struggles to shoot this caliber using a lightweight compact pistol, though she's not an experienced shooter. Some smaller, older, weaker, or disabled people may also have issues with it.
9mm is also the cheapest ammo of those considered sufficient for defense. This should hopefully allow you to spend more time practicing with your firearm and improving your skills.
When discussing 9mm pistol ammo, we're technically referring to 9X19mm Parabellum rounds. It's also commonly referred to as 9mm Luger, named after its designer, Georg Luger. If you're at the gun shop or range, you can simply refer to it as "nine millimeter" and they'll know what you mean.
Common Bullet Weights: 115 gr, 124 gr, 135 gr, 147 gr
Perhaps it's a loud minority, but gun enthusiasts seem to LOVE .45 ACP caliber pistols. It's clear visually that the .45 ACP is a solid step up from other common self-defense rounds in terms of its size. With this size comes increased damage to anything in its path.
Personally, I believe that magazine capacity is of greater importance for defense, especially if you were ever attacked by multiple people (though this scenario is extremely unlikely). You can always fit more 9mm rounds into a similarly sized magazine than .45 ACP rounds. Please note that you can NOT actually use ammunition other than what your firearm is intended to use. The point is that similarly sized pistols and their magazines can fit more rounds if they use a smaller caliber. The FBI seems to echo this sentiment, summarizing, "9mm Luger offers higher magazine capacities, less recoil, lower cost (both in ammunition and wear on the weapons) and higher functional reliability rates (in FBI weapons)," when testing different calibers. As the FBI mentioned, .45 ACP is also significantly more expensive than 9mm. Usually the cost of .45ACP ammo is $.28-.34/round.
Having said all of that, if you want to shoot a pistol chambered in .45 ACP, go right ahead. Many individuals will have little to no problems handling a handgun of this caliber. However, I would not recommend getting the average person started by shooting this caliber, especially those who are hesitant to shoot for the first time.
Due to the 1986 FBI Miami Shootout, which led to two killed and five wounded FBI agents, the FBI started looking to replace its standard issue revolver with a semi-automatic pistol. They began testing 9mm and .45 ACP calibers, but then found 10mm rounds to perform best by their metrics.
The FBI enlisted Smith & Wesson to design a 10mm handgun based on the existing large-frame Smith & Wesson model 4506. Smith & Wesson came to the realization that they could reduce the size of the 10mm cartridge by downsizing its primer. With the help of Winchester, Smith & Wesson created the .40 caliber round. This allowed it to fit within their medium-frame 9mm handguns, while maintaining the ballistic performance of the 10mm. The FBI used the .40 S&W rounds until 2015, due to the aforementioned reasons. Today the .40 S&W caliber is still commonly used by police and by civilians for self-defense. While .40 S&W bullets are smaller than .45 ACP, they have a higher velocity when shot. This results in the two causing very similar recoil, all other things being equal. Like with 9mm, .40 S&W will allow magazines of similar sizes to hold more rounds than .45 ACP.
