A jacketed bullet is a projectile with a soft metal core (usually lead) wrapped in a harder outer shell, typically made of copper or a copper alloy. The jacket serves two main purposes: it protects the barrel from lead buildup at high velocities, and it gives manufacturers precise control over how the bullet behaves when it hits a target. Nearly all modern rifle ammunition and most handgun ammunition designed for self-defense or military use features some form of jacketing.
Why Bullets Need Jackets
Pure lead is soft enough that it deforms under the extreme pressures and friction inside a gun barrel. At moderate speeds, this isn’t a problem. But once velocities climb past roughly 1,500 feet per second, bare lead starts smearing onto the barrel’s rifling grooves, a problem shooters call “leading.” This fouling destroys accuracy quickly and is difficult to clean. Early cartridge designers solved this by encasing the lead core in a thin shell of harder metal, allowing bullets to travel faster without damaging the bore.
Copper became the standard jacket material because it’s hard enough to resist deformation in the barrel yet soft enough not to wear out the rifling prematurely. Some manufacturers use gilding metal (a copper-zinc alloy) or, in newer military designs, steel with a copper wash. The jacket also lets engineers control what happens on the other end of the bullet’s flight: by adjusting how much of the core is covered, or by adding features like a hollow cavity at the tip, they can make a bullet that punches cleanly through a target, mushrooms on impact, or something in between.
How Jacketed Bullets Are Made
Most bullet jackets start as flat sheets of copper or copper alloy fed into a cupping press. The press punches out a small disk of metal and simultaneously shapes it into a shallow cup. For handgun bullets, that cup may already be close to the right proportions. Rifle bullets, where the jacket can be two or more times the bullet’s diameter in length, require additional steps called drawing. In drawing, the cup is stretched through a series of progressively narrower dies while a punch maintains constant contact with the walls, ensuring uniform thickness all the way around. This stack of dies keeps stresses even and controls concentricity, which is critical for accuracy.
Once the jacket is formed, a lead core (swaged from wire into the correct weight) is inserted, and the assembly is pressed into its final shape. Some designs bond the jacket chemically to the core through electroplating, which prevents the two from separating on impact. Others rely on mechanical pressure alone. The final step is shaping the nose profile, whether that’s closing the jacket completely over the tip, leaving a small opening for a hollow point, or exposing a bit of the lead core at the front.
Common Types of Jacketed Bullets
Full Metal Jacket (FMJ)
The most widely produced jacketed bullet. An FMJ has a lead core completely encased in a hard metal shell, with the jacket open only at the base (which sits inside the cartridge case). Because the jacket fully covers the nose, FMJ bullets don’t expand or deform much on impact. They penetrate deeply and predictably, which makes them the standard choice for military use, target shooting, and range training. The downside of that deep, narrow wound path is overpenetration, meaning the bullet can pass entirely through a target, which is why FMJ is generally a poor choice for self-defense or hunting.
Jacketed Hollow Point (JHP)
A JHP has a cavity engineered into its tip. On impact, pressure forces the jacket and core to peel outward like a mushroom, creating a wider wound channel while slowing the bullet down inside the target. This controlled expansion is why JHP is the dominant bullet type for self-defense and law enforcement. The tradeoff is reduced penetration through barriers like auto glass or heavy clothing, and hollow points are generally less aerodynamic at longer distances than streamlined FMJ designs.
Jacketed Soft Point (JSP)
A JSP splits the difference. The jacket covers the sides and base but leaves a portion of the lead core exposed at the tip. This exposed lead initiates expansion on impact, but more gradually than a hollow point. The result is deeper penetration with moderate expansion, a combination that works well for hunting medium to large game where the bullet needs to reach vital organs through muscle and bone before it begins to open up. Many hunters prefer soft points over hollow points for exactly this reason.
Jacketed Bullets and International Law
The distinction between these bullet types has legal weight. The 1899 Hague Declaration specifically prohibits military use of “bullets which expand or flatten easily in the human body, such as bullets with a hard envelope which does not entirely cover the core, or is pierced with incisions.” This is why military forces worldwide issue FMJ ammunition rather than hollow points or soft points. The declaration only applies to conflicts between signatory nations, and it has no bearing on civilian or law enforcement use. Police departments routinely issue JHP ammunition precisely because its expansion reduces the risk of a bullet passing through a person and striking a bystander.
Jacketed vs. Unjacketed Bullets
Plenty of ammunition still uses plain lead bullets with no jacket at all. Revolvers, many lever-action rifles, and low-velocity handgun loads work fine with bare lead or lead alloy projectiles. These are cheaper to produce and perfectly accurate within their velocity range. Some shooters use powder-coated lead bullets as a middle ground, where a thin polymer coating reduces leading without the cost of a copper jacket.
The practical line is velocity. Once you push past about 1,500 fps, unjacketed lead bullets foul the barrel badly and accuracy falls apart. Any cartridge designed to operate above that threshold, which includes virtually all centerfire rifle cartridges and many magnum handgun loads, needs either a traditional copper jacket or a modern alternative like a polymer coating to function reliably.
Newer Jacket Materials
Copper remains dominant, but environmental and cost pressures are driving alternatives. Some military programs have experimented with high-temperature polymer jackets paired with tungsten alloy cores instead of lead. These designs aim to match the weight and ballistic profile of traditional bullets while eliminating lead exposure for shooters and at training ranges. Steel jackets with a thin copper plating are common in imported military-surplus ammunition, offering lower production costs at the expense of increased barrel wear. For most civilian shooters, copper-jacketed lead-core bullets remain the standard, but the technology is slowly shifting as lead restrictions expand in certain states and countries.