My past consisted of shooting rifles and shotguns but my present shooting habits have expanded into handguns. As an author I took a leap and decided to include more technical information on the guns used in my latest book, The Walls of Freedom. I researched the guns I wanted to use in the story and as an individual with little experience in the handgun world, I assumed since the 9mm handgun referred to the ammo then a 45 handgun took a 45mm cartridge. In hind site this makes no sense since a 45mm bullet would be huge and you would need an elephant gun to shoot it.
Then I got feedback from my audience. Most folks would not notice the difference but to those educated in handgun specifics this error was like nails on a chalkboard. Here is some feedback I recieved:
"Hi Sara, I really enjoy the podcast, and your books are entertaining and fairly accurate, but there is one item you should go back and correct. That is the ammunition for the 1911 handgun in your latest book. The correct nomenclature for the round is .45ACP. The .45 is an inch measurement, and the ACP stands for "Automatic Colt Pistol". That equates to a bullet that is .450 inches in diameter in a brass case designed for the "Automatic Colt Pistol" not to be confused with the .45 Colt for the old school Colt Peacemaker Single Action Revolver that you see in nearly every western that has come out of Hollywood. Now the Russians fielded a 45MM towable anti-tank gun during WWII and the loaded complete cartridge was almost 18 inches long with a projectile ("bullet") diameter of just over 1-3/4 inches. A wee-bit too big for a 1911 handgun..LOL Best of luck to you, and thank you for all the hours of entertainment and knowledge your podcasts have provided. -Tim"
This feedback from Tim made some light bulbs go off in my head so I delved into researching what this .45ACP meant. This round was designed specifically for the Colt 1911 designed by John Browning in 1905. It is a short, rimless cartridge with a diameter of .452inches.
The closest cartridge to the .45ACP is the 9mm but there are some big differences as pointed out by Diffen.com. The 9mm bullet has a 9mm diameter but the .45ACP has a 11.5mm diameter. Both cartridges are rimless but the .45 case is straight and the 9mm is tapered. The .45 is generally more expensive than the 9mm. The .45 has more recoil but it also has more penetration and expansion. The 9mm will work in a smaller gun, has less recoil, a higher velocity and typically more of them fit in the magazine than with a .45ACP cartridge.
The next time you hear someone discussing "a 45" vs a "9mm" it will not be so confusing. Remember in The United States of America we use a different system of measurement than the rest of the world. Since the .45ACP was developed by Browning in the United States the .45 refers to inches. The 9mm was developed by George Lugar in Germany and thus the cartridge is measure in millimeters. Knowing the history and the specifics makes this topic an easy one to explain to a novice.
Notice that I didn't include any information on which one is best because that is an age old discussion that has been going on for many, many years and will continue to be hotly debated long into the future. Hopefully this gets you closer to understanding the needs of your firearm.
I am changing the nomenclature for this cartridge in future editions of The Walls of Freedom and thank everyone for pointing out the error and encouraging me to learn more.