Bullets

Every bullet type is designed for a specific purpose and the range of bullet designs available for a single firearm can be substantial. Figure 11.1 illustrates some different physical designs of round nose bullets.63 This only illustrates a variation of types within one design of bullet that is available in a range of calibers. Variation of types occurs within other designs of bullet, for example, truncated cone, cone- or spire-point, spitzer, flat nose, semi-wad-cutter, wad-cutter, round ball, and so forth, all of which are available in a range of calibers. Even the design of the base of the bullet can vary.64 This is illustrated in Figure 11.2.

There is also a wide variety of bullet core/bullet jacket designs without even considering compositional differences. Bullets are unjacketed, or

Unjacketed lead

Semi jacketed "soft point"

Semi jacketed "soft point"

F.M.J. with slits to improve expansion I_I

F.M.J. with slits to improve expansion I_I

F.M.J. with side slits

Unjacketed lead

Semi jacketed hollow point

Semi jacketed hollow point

,1111 , Semi jacketed with side slits

,1111 , Semi jacketed with side slits

Unjacketed with steel tip to improve penetration i

Unjacketed with steel tip to improve penetration i

Two piece bullet jacket cap covers hollow cavity

Two piece bullet jacket cap covers hollow cavity

F.M.J. with side slits

Unjacketed hollow point

Unjacketed hollow point

Figure 11.1 Designs of round-nosed bullets.

jacketed (envelope), or partially jacketed. Unjacketed bullets are usually confined to revolvers or low-power pistols and rifles. Such bullets may have their surface coated with a very thin layer of copper or brass colored material which is used as a lubricant, and for cosmetic reasons. This is referred to as a "coat" or "wash" and is not a bullet jacket in the conventional sense of the word. Unjacketed bullets are frequently lubricated with some form of wax or grease to prevent or reduce lead fouling in the barrel of the firearm.

Higher velocity bullets have to be either full or partly jacketed because an unjacketed lead bullet fired at high velocity can suffer deformation and have a detrimental amount of lead stripped from its surface by the rifling grooves. Such lead deposited inside the barrel has a pronounced effect on accuracy of subsequent shots. Unjacketed lead bullets are also prone to damage by the feeding mechanisms of self-loading firearms.

In the majority of bullets the lead base is exposed to the hot propellant gases. This applies to unjacketed and jacketed bullets (excluding total metal jacketed bullets). Some bullets incorporate a gas check in the base to prevent erosion by the hot gases. Such erosion can upset the symmetry of the bullet and consequently the accuracy. The base of the bullet may be filled or covered with a substance, for example, Alox base lubricant, that is unaffected by the temperature and pressure generated during discharge. Another method is to enclose the base with a shallow copper cup. Some bullets have the base enclosed by the jacket. Electroplated jackets usually cover the entire bullet and some soft point bullets with a nose of exposed lead have a partial jacket which is usually closed at the base. Bullets that are totally

Flat base

Boat tail

Hollow base (For Obturation)

Metal base (Gas Check)

Figure 11.2 Bullet base designs.

enclosed by the jacket, including their base, are referred to as total metal jacketed bullets (TMJ).

Conventional bullets are referred to as ball loads, the word "ball" originating from the use of round balls as projectiles in the early days of firearm development. Modern bullets are nonspherical projectiles for use in rifled barrels. Conventional bullets are designed for either penetrating power or stopping power (transfer of all kinetic energy on impact thereby rapidly stopping the human or animal target) or a combination of both. This is achieved by physical design and the selection of materials with suitable physical properties.

The bullet jacket material is almost always harder than the bullet core material, with the one exception of armor-piercing bullet jackets. Bullet jacketing is done either by electroplating or, much more commonly, the jacket is manufactured separately from the bullet, and the bullet then forced into the jacket in a press. Another method is to pour molten lead into the jacket. The edges of the jacket are usually partly rolled over the base of the bullet or attached by some other physical means.

Whenever a jacketed bullet strikes a target it is possible for the core and jacket to separate, with a consequent reduction in penetration. To prevent such an occurrence a variety of crimps, folds, jacket geometries, and melted core techniques are employed. Another method of interest to hand loaders is the use of a product called Core-Bond which is a flux that removes surface oxides allowing molten lead to bond directly to the jacket. This allows a degree of alloying between the two metals, which is claimed to provide bonding superior to that achieved by physical methods. Soldering of the jacket to the core has also been employed.65

Bullet jacket materials include gilding metal; cupronickel; cupronickel-coated steel; nickel; zinc-, chromium-, or copper-coated steel; lacquered steel; brass; nickel- or chromium-plated brass; copper; bronze; aluminum/aluminum alloy; Nylon (Nyclad), Teflon- and cadmium-coated steel (rare). Black Talon bullets have a black molybdenum disulfide coating over the metal bullet jacket which acts as a dry lubricant. Steel jackets are frequently coated both inside and outside as an anticorrosion measure. Gilding metal is by far the most common bullet jacket material. Tin is claimed to have lubricating properties and is sometimes incorporated in bullet jacket material. The alloy is known as Lubaloy or Nobaloy and contains 90% copper, 8% zinc, and 2% tin.

The thickness and hardness of the jacket can vary between the base and the nose of the bullet, with the nose portion thinner for better expansion on impact or thicker for greater penetration of the target. The way the jacket is physically attached to the core can vary. This depends on the desired effect of the bullet on the target, either the controlled expansion of the bullet, greater penetration of the bullet, or the prevention of core and jacket separation. Figure 11.3 illustrates some different physical designs.66

Winchester silver tip

Trophy bonded "bear claw"

Hornady FMJ Barnes super solid (Unjacketed)

Barnes soft point

Nosler partition

Trophy bonded ("Sledgehammer")

Figure 11.3 Bullet core/jacket designs.

The core of the bullet can be made from a variety of materials; lead is by far the most common because of its high density and the fact that it is cheap, readily obtained, and easy to fabricate. But copper, brass, bronze, aluminum, steel (sometimes hardened by heat treatment), depleted uranium, zinc, iron, tungsten, rubber, and various plastics may also be encountered. (When most of the fissile radioactive isotopes of uranium are removed from natural uranium, the residue is called depleted uranium. Depleted uranium is 67% denser than lead, and it is an ideal bullet material and is very effective in an armor-piercing role, both in small arms and larger munitions components. Because of its residual radioactivity its use is controversial.) Bullets with a lead core and a copper alloy jacket are by far the most common.

Sometimes a combination of bullet core materials is used to produce a hardness difference between the base and the nose (dual core bullets), for example, jacketed bullets with a lead nose and a steel base, a steel nose and a lead base, or a soft lead nose and a hardened lead base.

Bullet lead can be either soft lead or lead hardened by antimony, by tin, or by both. Mercury was also used to harden lead in the early days of bullet development. The quantity of alloying materials varies considerably, for example, antimony <0.5% to as high as 12% but typically 2% to 5%, tin <0.5% to 10% but typically 3% to 5%. A larger amount of tin is required to give the same degree of hardness as that of antimony; consequently, for cost reasons, antimony is more frequently used.

Some jacketed bullets incorporate a small cavity in the nose which is filled with a material different from the bullet core. In some bullets the cavity is unfilled. Bullet tips are usually made from lighter-weight material than that used for the core, for example, plastic, aluminum, fiber, sodium carbonate, polycarbonate, nylon, paper, mild steel. Some soft point and unjacketed bullets employ a metal cap over the nose of the bullet either for increased penetration, to protect the nose from damage, or to improve feeding in self-loading firearms. Copper, steel, aluminum, and plastic caps are encountered.

Non-ball bullet types are often referred to as "filled bullets" and are designed for special purposes, for example, tracer, incendiary, and armor-piercing roles.

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  • maximilian
    How dose copper coating effect lead hardness of bullets used in cap&ball revolver?
    5 years ago

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