Month: May 2018

Jargon: A Round Primer

Jargon: A Round Primer

Introduction to the Properties of Ammunition (Corrected)

With more than a little tongue-in-cheek, “A Round Primer” is about the properties of ammunition and not a treatise on the geometry of primers. Think McGuffy’s Readers for ammunition. In a previous post, we identified the four components of a round: bullet, case, propellant, and primer. Here, we are going to briefly explore what manufacturers mean by terms commonly used when referring to ammunition. Terms such as “caliber,” “gr,” or “grain,” “velocity,” and “energy,” and others are the focus of this discussion.

Caliber

In small arms, caliber is the approximate internal diameter of the barrel’s bore. In English units, caliber is represented by fractions of an inch. For example, a .22 caliber firearm has bore diameter of approximately 22 hundredths of an inch (or .22). A .45 caliber firearm has a bore diameter of approximately 45 hundredths of an inch (or .45). In metric units, caliber is typically represented in millimeters (mm). Common examples are 7.65 mm, 9 mm, or 10 mm. However, we must be aware that caliber is only part of a cartridge’s designation. Just to make things more confusing, bullets are a few thousandths of an inch larger than their corresponding bore diameter (see the 5.56 x 45 mm below).

Cartridge Nomenclature

For many cartridges from the era of black powder, nomenclature is a function of the caliber and the typical amount of black powder used as a propellant. For example, the rifle cartridge .45-70 was a .45 caliber bullet propelled by 70 grains of black powder (we will get to “grains” in a moment), and the rifle cartridge .44-40 was roughly a .44 caliber ball propelled by 40 grains of black powder. Pistol cartridges of the black powder era generally were identified by a number and a name, for example, .38 Smith and Wesson. Occasionally we see the older conventions continue to be used with smokeless powders. Examples include the .45-70 and the .30-30 even though both cartridges are now loaded with smokeless powder.
Today, cartridge nomenclature is largely a function of the cartridge designer, or standardizing agencies. Thus, we see a .257 Roberts, .30-06 (a .30 caliber round adopted by the U.S. Army in 1906), and a 5.56 x 45 mm (a 5.7 mm caliber bullet in a 44.70 mm case adopted by NATO in 1980).

Birds of a Feather
Another wrinkle in the nomenclature category is that of multiple ways to refer to the same cartridge. For example, 9mm Luger, 9mm Parabellum, and 9x19mm all refer to the same cartridge. .45 Auto, and .45 ACP are two other examples of different designations for the same cartridge. Some handguns designed (typically called “chambered”) for one cartridge may be used with others. For example, the .44 Remington Magnum can safely shoot the .44 S&W Special, and the .357 Magnum can safely shoot the .38 Special.

Almost Only Counts in Horseshoes and Hand Grenades (Corrected)
However, you must also be aware that similar names are not necessarily interchangeable. For example, the .300 Winchester Magnum and the .300 Weatherby Magnum cannot be used interchangeably.

Note especially there are some firearms that are interchangeable in only one direction. For example, rifles chambered for 5.56x45mm NATO can safely shoot .223 Remington, but they are not reversible. That is, a rifle chambered in .223 Remington CANNOT safely shoot a 5.56x45mm NATO cartridge. On the other hand, commercial rifles chambered for the .308 Winchester can shoot both the .308 and the 7.62x51mm NATO cartridge safely, but not all rifles originally chambered for the the 7.62×51 NATO round can shoot the .308 Winchester, safely.

To get around the one-way interchangeability, some designers developed new chamber dimensions to accommodate both calibers. For example, the .223 Wylde is a relatively new design that allows you to shoot either the .223 Remington, or the 5.56x45mm NATO round, safely.

In the final analysis, you, the shooter, are responsible for knowing what caliber your firearm is designed to shoot, and for only using ammunition designed for your firearm. READ YOUR MANUAL!

Grains

The term “grains” frequently causes confusion for novice shooters. To keep things simple, we will discuss what the “grains” or “grn” label on a box of modern, smokeless ammunition means. Fundamentally, “grains” refers to a bullet’s weight, where there are 7,000 grains to a pound, or 437.5 grains to an ounce.

Shown here are typical end-caps on three boxes of factory ammunition.

The box labelled “American Eagle” is a .45 Auto. The “230 grain” refers to the weight of the bullet. “Full Metal Jacket” refers to the bullet’s characteristics, which in this case typically means a round nose lead bullet fully encased by a copper alloy jacket. The box labelled “Federal Premium” is a 9mm Luger with a bullet weight of 124 grains. The bullet profile is Federal’s “HST” JHP (Jacketed Hollow Point), which in this case indicates a bullet with a copper alloy jacket that is formed with a deep conical cavity in the nose–the hollow point. The box labelled “Corbon” is a .380 Auto with a bullet weight of 80 grains and with Corbon’s DPX bullet profile (essentially a jacketed hollow point).

Velocity and Energy

Two other pieces of data you may see on a box of factory ammunition are the bullet’s velocity in feet per second (fps) and energy in foot-pounds (ft-lbs). Most manufacturers identify typical velocity and energy as they are measured at the muzzle (aka muzzle velocity and muzzle energy), although many will provide typical measurements at other ranges, as well. For example, Winchester’s target 9mm Luger, 115 grain, FMJ has an advertised muzzle velocity and energy of 1190 fps and 362 ft-lbs. At 5 yards, they are 1176 fps and 353 ft-lbs, and at 25 yards are 1125 fps and 323 ft-lbs.

Ammunition manufacturers design cartridges for specific uses and performance features. What is suitable for target practice is very likely not suitable for hunting or personal defense applications. In the end, the responsibility for choosing the proper ammunition for a specific purpose and firearm is yours–the shooter. Always ensure the ammo you select is designed for your specific firearm!