Ammunition terminology can be daunting for new shooters. One term that you’re likely to come across quite frequently is “hollow-point.”

What Is Hollow-Point Ammunition?

A round of 10mm hollow-point ammunition that has "mushroomed" after impacting a target.

The metal surrounding the cavity of a hollow-point round expands or “mushrooms” out upon impact with flesh or other fluid materials.

Hollow-point ammunition contains a divot in the very tip of the bullet. Upon impact with soft materials — such as flesh — the material fills this cavity and causes the surrounding rim to mushroom out. The standard acceptable expansion is 1.7 times the original diameter of the projectile. So a .45 ACP hollow-point (with an original diameter of 0.451 inches) should expand to at least 0.7667 inches. Some rounds expand to nearly twice the original size, dependent on the design and composition of the projectile and the muzzle velocity when it impacts the target.

Why Would Someone Choose Hollow-Point Ammo?

The expansion of a hollow-point bullet generates two main effects.

  1. A larger diameter bullet produces a wider wound channel. Increased blood loss leads to a faster drop in the target’s blood pressure — hopefully ending the threat more quickly. Remember, the point of legal self-defense is to stop the threat as quickly as possible.
  2. The loss of velocity decreases the chance of over-penetration. When a hollow-point bullet mushrooms, it expends considerable forward momentum. This helps to keep the round from continuing through the target and potentially hitting an unintentional victim in the background.
A jacketed 10mm hollow-point bullet showing both the outer copper jacket and a cutaway of the lead, hollow-pointed core.

This Jacketed Hollow-Point (JHP) round involves a copper jacket over a lead core. Notice the hollow cavity in the lead at the tip of the bullet and the serrations at the top of the copper jacket.

What Are the Downsides of Hollow-Point Ammo?

The limited penetration mentioned above could fail to produce a wound serious enough to stop an attacker. Barriers such as thick winter clothing or moderate cover would exacerbate this problem. Alternatively, it is possible for clothing or other materials to get caught up in the hollow tip of the bullet, impeding expansion.

The FBI prescribes a minimum of 12 inches and a maximum of 18 inches as the optimal depth for bullet penetration in a human target. Once again, muzzle velocity greatly impacts not only how well a bullet expands, but the depth to which it will penetrate.

Will Your Gun Take Hollow Points?

Some rifles and pistols, especially semi-automatics, may have trouble feeding hollow-point rounds. While most modern handguns are designed to accept a wide variety of ammunition, hollow-points may cause some to misfeed or jam. Be sure to test specific brands in your gun — especially if it’s the firearm you intend to carry every day. A crucial self-defense moment is no time to discover that your carry gun doesn’t like to fire hollow points.

The Legal Issue of Hollow Points

While most police departments throughout the country issue hollow-point ammo to officers (to cut down on that pesky overpenetration described above), some states have made it illegal for use by civilians. As we often state on this blog, be sure to know your local laws regarding firearms and ammunition.