But what is 9X19mm or 9mm Luger or 9mm Parabellum?
As was said... they are different names for the same thing... But to break it down a little.
When people talk about 9mm, most of the time they are talking about the standard NATO 9mm pistol round. As it is the most common 9mm caliber round.
is the metric standard designation. The first number is the caliber/diameter of the bullet in mm and the second number is the length of the cartridge case in mm.
is another name for it. Because one of the first and most popular pistols chambered for it was the German Luger pistol.
was the original designation for the round. Parabellum is Latin and translates to "For War"
may be used as well... but be careful
. Ammo marked NATO and
also marked with the NATO stamp on the cartridge case is actual military issue/surplus... they tend to be higher pressure or more powerful... this is doubly true for ammo designed for machine gun use, as it is loaded to even higher pressures and power. As a new shooter, stay away from ammo marked "NATO" or any ammo that has a small circle with a cross in it stamped on the bottom of the round/casing. If the box it comes in is marked NATO and generic looking, it is possible true NATO military rounds. If it is in a retail box and does not have the NATO head stamp you are fine. (the stamp on bottom of the case is called the head stamp) Winchester Ranger is an example of NATO stamped ammo that is not military issue.
Notice the case on the right... the circle and cross is the NATO head stamp used on military rounds.
use any other ammo in your pistol... the names listed are it... no others.
There are Other 9mm caliber rounds that can be called 9mm... and should not be used in your pistol. I will list them here so you do not use them by mistake.
9x18mm or 9mm Makarov... are the same round. It is a Russian designed round. The Makarov pistol was the pistol designed to shoot this round, hence the name.
9x17mm is the metric designation for the .380acp round... also called .380 Auto, 9mm Browning, 9mm Corto, 9mm Kurz, 9mm Short.
There are actually more... but they will not fit into the chamber of the pistol, and are less common, so you should be fine.
For general plinking and range shooting... the 115gr FMJ is the most common and generally cheapest. $10-15 per 50rd box depending on brand and where you shop. For fun, the cheap stuff is fine... experienced shooters can notice accuracy differences between brands and bullet weights, but new and average shooters will not. You do not NEED to use other weight rounds unless you want to...
Hollow Points are for defese use... not target shooting... but if you are using the pistol for defense in the home, you should shoot a few boxes of the brand hollow points you plan to use. This is to make sure they are reliable in the pistol. They are not all the same in design/shape, so they do not feed the same. The Sig should feed most if not all without issue, but test your chosen brand any way.
+P is a designation that means the rounds are loaded to higher pressures and power than the original standards. It is an officially recognized specification that has a min/max pressure rating.
+P+ is a designation that usually means it is loaded to pressures higher than even +P... but it IS NOT an officially recognized standard... some use them... I do not. Its not an official thing, so I don't risk it.
Not all pistols can shoot +p and +P+... the instruction manual will tell you if it is ok or not. Regardless of whether or not the manual gives the ok... +P and +P+ will cause more wear and stress on the pistol and its parts than normal ammo... so shooting a lot of them is discouraged.
115gr refers to the wieght of the bullet/projectile measured in grains... Grains are very small units, there are 7000 grains in a pound, or 15.43 grains per gram.
Bullets are usually lead surrounded by a jacket of copper... this is almost always true... Though you can get rounds that are pure lead with no jacket. 9mm lead rounds are not common in the retail market. There is also a pure copper round, but it is a very light round and is a specialty hollow point design. Some manufactures also make lead free "clean" rounds for use in ranges that do not allow lead... they tend to be expensive.
The case that holds the bullet, powder, and primer is usually made of brass... You can find ammo with aluminum cases. They tend to be cheaper than brass cased...
There is also ammo that has steel case. It is a mild/soft steel, it is usually the cheapest you can buy. It is made in Russia mostly, and can be less reliable. Mostly because of hard primers that do not like to fire in some pistols... and quality control and consistent manufacture are the other common things people complain about. New manufacture Wolf brand steel cased seems to be the best of the steel, followed by the Silver bear... then Brown Bear, then lastly Tula... New Wolf and Silver Bear use steel that has a thin polymer coating that aids in reliability... the others use a Lacquer that can be uneven and even melt in a hot barrel.
I hope that answered some questions.