What Does “Caliber” Mean?

A weapon’s “caliber” is the size (usually the diameter) of the ammunition that it will accept.

That sounds simple, but it is not that easy.  Sometimes different names are uses for the same ammunition.  Sometimes cartridges are listed in metric sizes and sometimes they are listed in inch sizes.  If that isn’t confusing enough, some ammunition is described by  the cartridge length.

An example of this is ammunition for the 9MM pistol. You can find ammunition listed as 9MM, Parabellum, or 9 X19. They are the same.

The best way to tell what you should buy is to examine your firearm. The ammunition that the firearm will accept is stamped on the barrel or frame of the weapon. Also consult the manual that came with your firearm. If you do not have the manual, go online. It is there. Look for it and stick to it. Do not put ammunition into a weapon that will overload the barrel or chamber. Do not put magnum loads in a pistol that will not tolerate the extra pressure. Keep it simple. If it isn’t listed on the firearm or in the manual, don’t use it!

Another point of confusion is the shape of the nose of the bullet. There are several choices for several purposes. Target practice is usually conducted with flat, lead (wad cutter) rounds or with round nose rounds (ball ammunition). This is the cheapest as it is the easiest to produce. Carry ammunition is usually hollow point ammunition as it has a very predictable pattern as it enters and spreads through a target.

Now to the weight of the bullet. It is expressed in grains. The heavier the bullet weight, the more expensive the ammunition. The theory is that the heaver the grain the better the stopping power. This makes the bullet travel slightly slower and impacts the target with a higher powered punch.

9MM ammunition is available in bullet weights of 115, 124, or 147 grains. The practice 9MM ammo is usually 115 round nose (ball) with a full metal jacket.