Choosing the right gun (and corresponding caliber of ammunition) has everything to do with your intended use of the gun. If you’re planning to use it for self-defense, there are things you’re going to look for in the type of gun – as well as the type of ammunition – you purchase that you wouldn’t need to consider for target shooting.
Assuming you’re looking to purchase a self-defense handgun, let’s compare two popular conceal carry caliber choices. 9mm and .380ACP are both 9mm in diameter; where they differ in size is in length. .380ACP is 17mm long, whereas 9mm is 19mm long.
Keep in mind that user familiarity with the pistol and practice shooting will always largely determine the outcome of any shot, so these are very general statements. Any scenario can be largely impacted by the amount of practice the gun owner has with the particular gun they are shooting, as more practice should make them more comfortable and accurate when shooting.
A .380 is considered an ultra-compact carry pistol because of its small size. It is easily concealable but as such, it won’t be as powerful as a 9mm. It’s a smaller gun with a smaller bullet, making it all-around more compact than a 9mm.
A .380 handgun will be harder to aim and shoot accurately than a bigger gun simply because of its small size. What it lacks in stopping power, however, it makes up for in concealability. .380s are good for protecting yourself at short distances. Although it won’t penetrate the way a 9mm bullet would (if shot with the same accuracy), it’s going to be more easily concealable than a 9mm.
A 9mm bullet in the U.S. is considered a 9x19mm size. 9mm is approved for use by law enforcement and the military in the United States. 9mm will generally have more stopping power than a .380, although there are always several other factors to take into consideration.
9mm handguns are larger than .380 handguns, which means they should be easier to aim and shoot with greater accuracy. 9mm bullets will generally penetrate more deeply, as well, simply because of their higher grain count and velocity.
Penetrability and concealability are both are worth considering when protecting yourself in a real-life scenario. Ask yourself how important is it to you to have easy access to your small conceal carry gun when walking through a dark alley alone at night, for example. Being able to carry an undetected, smaller gun on your person could be just as important of a factor in having a favorable outcome – depending on the distance, size, speed of the attacker – as it is to have a larger caliber that might travel further and faster.
There are other things to take into consideration besides caliber size when picking ammunition. Do you want hollow point or full metal jacket (FMJ), for example? Hollow point bullets are meant for expanding inside the target once ejected from the gun, therefore making them deadlier.