Cartridges

A cartridge is a self contained collection of the expendable material needed to fire a gun. The first cartridges were paper tubes containing pre-measured gunpowder and a projectile. They were used in conjunction with muzzle loaders.

The paper was torn open and some of the powder was used in the priming pan. The rest of the powder was poured down the barrel followed by the projectile (usually a ball). The paper tube was crumpled up and put in the barrel as well, to keep the ball from rolling out. Paper, ball, and powder were tamped down by the ramrod.

Metallic Cartridges

In 1845 French inventor, Louis Nicolas Flobert created the first modern metallic cartridge by placing a small lead ball in a percussion cap. This was a significant development. All the expendables needed to fire a breech loading gun were now self-contained, safe to handle, durable, and could be loaded as a unit.


.22 short

The .22 Short was developed in 1857 for Smith and Wesson's new revolver. This is a rimfire, meaning that the priming compound is in the rim of the cartridge. They are still manufactured.

Rimfire is no longer popular, except for .22 and a few other odd cartridges, because the base of the case needs to be thin enough to be crushed by the firing pin.  This also means that the case can not withstand the high pressure needed to achieve high velocity.  The answer is center fire, which has the additional benefits of high reliability and reloadability.


Centerfire Cartridge

A percussion cap was placed in the center of the base of the cartridge case.  This allowed the base to be made strong enough to withstand much higher pressure. It also concentrated the priming compound in one place, as opposed to being distributed around the rim.  The development and manufacture of primers was now separate from that of cartridges leading to more reliability and adaptability.


Metallic cartridges allow breech loading; loading from the back end of the barrel, as opposed to muzzle loading; loading from the front end of the barrel. Breech loading with metalic cartridges was not only much faster but also paved the way for magazine fed firearms or repeaters as they were often called.


Cartridge Components

The components of a cartridge are the Cartridge Case, Primer, Powder, and Bullet. The case holds it all together.

A cartridge must fit the gun from which it is to be fired. The place in the barrel where the cartridge sits during the process of launching a bullet down the bore is the chamber. Every gun is manufactured with its chamber cut to industry standard dimensions for the intended ammo. This is said to be its chambering. (Chambers and cartridges that don’t meet industry standards are called wildcats and the ammo for these must be specially made. Many standard chamberings were once wildcats.)

Each chambering has a unique name. Thus you would say that an M1 Garand is chambered for .30 –’06 or your deer rifle is chambered for .30-30. Note that there is usually a family of different cartridges for each chambering. The differences are the weight and shape of the bullet, and the amount and burn rate of the powder. (Although the powder burns in milliseconds there are hundreds of different powders with carefully controlled characteristics to meet different needs.) It is possible to fire any of the family of cartridges from any gun with that chambering, with a few exceptions. (There are always exceptions.) For example .30-’06 is available with 150 grain (7000 grains per pound) spitzer (pointy) bullets, 168 grain match bullets, 180 grain soft point hunting bullets, and many more.

As noted earlier, chamberings have names. Many of the names sound like calibers or include the caliber in the name, but it is important not to confuse the two. It is the chambering of your gun which must match the ammo. The name of the chambering is often stamped right into the barrel.

.30 caliber cartridges

The six cartridges to the right are all .30 caliber. No two of them can be fired from the same gun. This is because they are all different chamberings. From left to right: .30 Caliber Carbine, 7.62 x 39 Russian, .30-30 Winchester, .308 Winchester (AKA 7.62 x 51and 7.62 NATO), .303 British, .30-'06

Note: When speaking the name omit the decimal point and say "by" for the x. Examples: seven six two by fifty one, thirty caliber carbine. .30-'06 is pronounced "thirty ought six".

There is no comprehensive system of naming chamberings. One of the following is often the case:

  • The name is a combination of the caliber and the year it was introduced. .30-’06 for example.
  • The name is a combination of the caliber and the original powder charge. .45-70 for example, where 70 stands for 70 grains of powder.
  • The name is a combination of the caliber and a name chosen by the inventor. .32 Winchester Special for example.
  • Then name is a combination of a pseudo-caliber and a name chosen by the inventor. 224 Weatherby Magnum for example.

What do I mean by pseudo-caliber? Consider the following chamberings: .218 Bee, .222 Remington, .223 Remington, .224 Weatherby Magnum, .225 Winchester.

Based on these names you might think I am talking about five different calibers. In fact they are all .22 caliber. It is the chambering that must match your firearm. A cartridge with the correct chambering will include a bullet of the correct caliber.

Another example is the venerable .38 caliber revolver. Almost every cartridge we know as .38 caliber is in fact .35 caliber. The .380 Auto, .38 Super Auto, .38 S&W, .38 Long Colt, .38 Special are all .35 caliber. This is because they evolved from the .38 Short Colt which used a .38 caliber heeled bullet.

A heeled bullet is one where the part of the bullet that fits inside the case, the heel, is smaller than the part that sticks out of the case, which has the same diameter as the case. The heel of the .38 Short Colt was .357" in diameter; just right for a .35 caliber barrel. When heeled bullets became obsolete for production reasons, the .38 turned into a .35 but kept the name. .22 rimfire is the only ammunition still made with heeled bullets.

Some chamberings are known by more than one name. The name is printed on the box of ammunition. Some common chamberings with multiple names:

  • 9mm Luger - 9mm Parabellum - 9 x 19
  • .380 Automatic - .380 ACP - 9mm KURZ
  • .223 Remington - 5.56 NATO - 5.56 x 45
  • .308 Winchester - 7.62 NATO - 7.62 x 51
  • .45 Automatic - .45 ACP (ACP stands for Automatic Colt Pistol)
  • .30-30 Winchester - .30 WCF - 7.62 x 51R
  • .30-'06 Springfield - 7.62 x 63
  • 8mm Mauser - 8 x 57 JS - 7.92 x 57 - 7.9 x 57

Some firearms can shoot more than one type of cartridge. Some examples:

  • Most firearms chambered for .357 Magnum can also fire .38 Special (The reverse is not true. .357 Magnum cartridges can not be shot from a firearm chambered for .38 special.)
  • Many firearms chambered for .22 Long Rifle can also fire .22 Long, .22 short, CB Caps, and BB Caps. (CB stands for Conical Ball and BB stands for Bulleted Breech. Who comes up with this stuff?)

Read the manual. Just because it is safe to fire an alternate chambering does not mean that it will feed correctly. In semi-autos, lower power cartridges may not cycle the action.


Primers

Primers come in five sizes and several varieties.

Sizes

  • Small Pistol
  • Large Pistol
  • Small Rifle
  • Large Rifle
  • Shotshell

Varieties

  • Magnum
  • Match
  • Bench Rest
  • Military
  • Muzzle Loader

Combinations are also possible.

(Don't panic: If you buy commercially produced ammunition it will have the correct primer.)

In the past priming compounds were corrosive, meaning that they left residue in the bore that tended to cause corrosion, damaging the barrel. There is still a lot of surplus ammunition with corrosive primers on the market. If you shoot this ammo you should clean your firearm as soon as possible.

Wikipedia article with info on primers.

Powder

The first cartridges used gunpowder also known as black powder. Gunpowder created a lot of smoke, a lot of fouling, and corroded gun barrels.

Modern cartridges use smokeless powder. Smoleless powder isn't smokeless but it does smoke less. That's right, seedless grapefruit have seeds and smokeless powder makes smoke. Such is life.

In 1846 Christian Schönbein treated cotton with nitric acid creating the first smokeless propellant called guncotton. Unfortunately guncotton proved to be rather unstable and many of the early factories blew up. The prevalence of the smoking remains of smokeless powder factories dotting the European countryside tended to dampen enthusiasm for further research. It wasn't until 1884 that Paul Vieille created a smokeless powder that was stable enough to be widely used.

All smokeless powders are nitrocellulose variations. Powders that contain only nitrocellulose are called single-base. Powders that also contain nitroglycerin are called double-base.

Today there are hundreds of different smokeless powders available for manufacturers and reloaders.

More than you ever wanted to know about smokeless powder.

Cases

Cartridge cases are the main component of ammunition. They hold the powder, primer and bullet. A less known function is to seal the breech against high pressure gasses. As we say in the northeast; "wicked high pressure."

Firearm chamber pressures are measured in Copper Units of Pressure or CUP. Little copper pellets are placed in a device operated by gas pressure supplied via a hole in a test barrel. When a round is fired the device crushes the copper pellet to some extent, in proportion to the pressure. The calibration is intended to be approximately equal to Pounds per Square Inch or PSI.

Chamber pressures range from less than 6,000 PSI for low powered handguns to more than 60,000 PSI for high powered rifles. For comparison, car tires are inflated to 30 PSI and aluminum SCUBA tanks are filled to 3,000 PSI.

When a gun is fired, this high pressure expands the case against the chamber walls, keeping the gasses from escaping out the back.

Cases are most often made of brass but steel and aluminum are getting more common for inexpensive ammunition. Metal-Plastic hybrid cases are also in use.

Cases can also be separated into two categories based on the type of priming they use.

In Europe most cases are Berdan primed. In this system there are two flash holes in the primer pocket along with the anvil which is part of the case. They are hard to reload and it is not often done in the US.

In the US Boxer primed cases are the norm. This system has one flash hole and the anvil is part of the primer. Brass, Boxer primed cases are easy to reload with a few hundred dollars worth of equipment. Reloading saves money and gives you total control over the variables allowing for more accurate, purpose built ammo.

Besides the type of priming there are some other case variations. Straight walled vs necked down (bottle necked), rimmed vs rimless, tapered, rebated, belted, and plated.

  • A straight walled case is the same diameter at its mouth (the open end) as it is at its base.
  • A necked down or bottle necked case has a larger diameter body, where the powder goes, and a smaller diameter neck, where the bullet is seated. This is to allow more powder in a shorter case.
  • Rimmed cases have a rim of a larger diameter than the case. The rim facilitates extraction.
  • The base of a rimless case is the same diameter as the case, but it has an extraction groove cut around the base making it look like a rim.
  • Rebated cases are smaller in diameter at their base. This is done to create ammo to fit an existing bolt face. These also have an extraction groove.
  • Tapered cases are slightly smaller at the mouth end and grow uniformly toward the base.
  • Belted cases have a short larger diameter section just ahead of the extraction groove. This adds strength and a surface for headspacing.
  • Sometimes cases are plated with nickel to prevent corrosion.

Bullets

There are more types of bullets than you can shake a stick at.

Lead is used because it is high in density and relatively inexpensive. At higher velocities lead tends to stick to the inside of the barrel. To prevent this, high velocity bullets are jacketed, or semi-jacketed with a harder material, most often a copper alloy.

The study of bullets in the firearm is called interior ballistics.

The study of bullets from the firearm to the target is called exterior ballistics.

The study of bullets after reaching the target is called terminal ballistics.

Bullets are made in different ways for different purposes. For example, match bullets are made to maximize shot to shot consistency with no regard for terminal ballistics. Hunting bullets, on the other hand, are designed to produce quick, clean kills on the intended game. In other words terminal ballistics is the main concern.

Each of the manufacturers below makes several types of bullets in many calibers.

Sierra

Speer

Hornady

Remington

Winchester

Nosler

Barnes

Berger

Lapua

Cast Performance

Bullets are bigger than their caliber by a few thousandths of an inch. Bullets are made to the diameter of the grooves in the intended barrel, or up to .003" bigger.

The ballistic coefficient (BC) is a measure of how much a bullet is affected by air resistance. .5 is a very good BC for a rifle bullet. Bigger numbers are better. Bullet shape, and weight relative to diameter, are the major factors affecting BC. At short range BC doesn't matter.

Special purpose US military ammo has color coded bullets:

  • Black - Armor piercing (AP); designed to penetrate armor, disable vehicles and chew up structure.
  • Red or Orange - Tracer; designed to light up so you can see where they go. (The other guy can also see where they came from.)
  • Blue - Incendiary; designed to light stuff on fire.


SAAMI cartridge and chamber dimensions.

Cartridge Collector's Exchange