In recent years the rules of firearms safety have been edited down so that there are now what is considered to be the 4 Rules of Gun Safety. These so called 4 Rules overlook one of the most important rules of safety with firearms, one that seems to be common sense to those familiar with guns, but yet may not be all that much mumbo jumbo to those unfamiliar with firearms. The important rule of which I write is:
Always be absolutely sure to use the proper ammunition in each firearm you are shooting. Now while this may seem like common sense, the topic of using proper ammunition can be confusing to a newcomer. It can be confusing because there are often several different sizes of ammunition with similar names. If for example you have a 9MM pistol, you can find 9MM Luger, 9MM NATO, 9MM Largo (also called long), 9mmShort (also called Corto, Brevia and so on). Some of these are the same as one another, others are quite different. Many other calibers of ammunition also have names or numbers close enough to one another to be confusing. The down side of using the wrong ammunition is that it can jam your firearms, can cause damage to the firearms, and can cause injury to the shooter.
The best ways to make sure that you are using the correct ammunition (in modern commercial firearms) is to check on the gun itself, or check in the manual for that particular firearm, or contact the manufacturer. Most commercially made modern firearms are stamped (marked) with the caliber size somewhere on the metal surface of the firearm. When you buy ammunition make sure to buy a box full of ammunition that has the same caliber marked on the box as is marked on the gun itself, or that is in the manual for that gun.
It is a simple rule, but the large amount of ammunition types out there that have similar numbers to designate their calibers and cartridge sizes can be somewhat of a boondoggle for the novice to have to figure out. If you are still uncertain after looking at the firearm, and are still uncertain after reading the manual, then call the manufacturer if still in business. If not still in business, then you may have to go to a competent firearms retailer or gunsmith to determine the correct ammunition for your gun. Don't rely simply on posting a question online in a forum or chatroom, don't make a guess, don't ask a friend who is unfamiliar with that type of gun, and so forth.
Remember that with any firearm, mostly military ones though, the actual firearm may have been modified to accept a caliber other than that for which it was originally intended. Some of these are marked (they all probably should be) and others are not can be changed, and these may have to be checked by a competent gunsmith before firing. I do not recommend buying such by the novice, stick to commercially manufactured guns first, until you have learned more about them, or at least buy a gun certified by the dealer to be in the caliber as it is sold.
Another thing you may want to avoid, especially when new to firearms, is reloaded ammunition. Many firearms enthusiasts, and some businesses, reload spent shell casings, so that they can be fired again. It saves money because new shell casings are expensive, and so is newly manufactured ammunition; the components are less expensive when you do the work yourself. The problem that can arise here is if a round (or rounds) were given an improper powder charge. This can lead to various problems, that includes injury to the shooter. Unless you are thoroughly trained in how to reload ammunition, don't do it. It might also be wise not to accept reloaded ammunition from others, unless you know they reliably reload to factory standards.
As I said above, this is one of the most important rules of firearms safety, so please don't forget to only use the proper ammunition in your firearms.
All the best,
2 hours ago