Here are four of the most popular Semi Auto Defsnsive Cartridges today, a comparison of size, and some history on each.
The .380 Auto Colt Pistol (ACP) also known by 9x17mm is popular in very small concealable handguns, while not the most powerful it has come a long ways in recent years that many people do use it for defense. The round was developed in 1908 for a pocket fired hammerless pistol—it actually was not hammerless, rather had an internal hammer similar to today’s Ruger LCP or Smith & Wesson M&P EZ. There are police departments that authorize this as a secondary firearm round due to its concealablity.
Above from Left to Right .380 ACP, 9x19mm, 40 S&W, .45 ACP. Graph paper used as a reference for relative size.
The 9mm Parabellum also called the 9mm Lugar is probably the most poplar defensive cartridge in the world. It was invented in Austria by Georg Lugar in 1901. It is often designated by 9x19mm. The 9×19 can be found in many countries and is the standard for NATO military pistols. Today it is one of the premier calibers for personal defense offering the right amount of power, low recoil and capacity.
The .40 Smith & Wesson (S&W) took the Law Enforcement world by storm in the early 1990s. Smith & Wesson with Winchester developed the cartridge for the FBI in late 1980s. The FBI had tested the 10mm cartridge as a replacement to their .38 Smith & Wesson Special. Full power 10mm was tough for a lot of people but a lower powder 10mm did work. S&W tried cutting the 10mm down to fit that amount of powder and now we have a .40 S&W. Smith and Wesson was not first to the market with a firearm for thier cartrige Glock beat them with the Glock 22 & 23 but Smith did release a 40 cal that year called the Model 4006. The 40 S&W remains a great defensive round with excellent history.
The .45 ACP has been around since 1904 when it was invented for Colt by John Moses Browning. It was developed because the .38 Long Colt that was being used by the military at the time lacked stopping power needed. It was then used in the Automatic Colt Pistol (hence ACP) . That pistol became the famed M1911 that lasted many years in the military inventory. According to a personal friend who has attended many post-mortem exams after officer involved shootings the 45 still has excellent penetration without over penetration. The one down side is you hold less capacity than a 9×19 or a 40 S&W in most platforms.
Which one will you choose?
—Castle
