Selecting a firearm for self-defense or hunting isn’t always easy, especially when you dive into terminal ballistics, and the wounding factors of different calibers.
Wounding factors vary based on the bullet’s diameter, design, velocity, and shot placement. Full metal jacket (FMJ) bullets typically inflict similar entry and exit wounds, whereas jacketed hollow point (JHP) and soft point (SP) bullets are designed to produce wider exit wounds.
This article will help you understand the terminal ballistics (i.e. wounding capabilities) of various bullet calibers and designs.
Disclaimer: Predicting the exact size of a bullet wound, especially an exit wound, is not possible with certainty. Too many variables are at play, including bullet design, impact velocity, barrel length, angle of impact, shot placement, clothing, and the density of the tissue struck. A bullet may not produce an exit wound at all, especially if it is a modern jacketed hollow point designed to expand and remain inside its target.
The information in this article is intended as a general overview of ballistic principles and approximate comparisons between calibers; not as a definitive guide to real-world wound outcomes. Every shooting incident is unique and cannot be reliably predicted or replicated.
Best Self-Defense Caliber and Damage to the Human Body
No caliber is effective for defense without proper shot placement. That being said, certain calibers are more effective for defense than others.
The best self-defense caliber is the one you can fire most competently. For example, .22 rimfire cartridges are quite small and have little power compared to others, but their low recoil facilitates accurate shot placement.
Conversely, larger cartridges’ stronger recoil complicates fast follow-up shots, but they compensate for that shortcoming by striking harder and inflicting broader wound channels.
With experience and proper training, such cartridges’ superior ability to inflict damage (colloquially known as “stopping power”) makes them preferable for everyday carry.
Some of the best handgun cartridges for self-defense are:
Effectiveness of Bullet Wounds: How Gunshot Wounds Work
To understand a bullet’s efficiency at incapacitating a target, we must have some basic understanding of the mechanics of wounding; i.e. how damage to the human body works. Four major factors contribute to the effectiveness of a bullet:
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Penetration - Measures the amount of tissue through which the projectile passes, and which it disrupts or destroys. A bullet’s capacity for penetration is commonly referenced as “sectional density.”
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Permanent cavity - Measures the volume of space, once occupied by tissue, that is destroyed by the passage of the projectile. It is a function of penetration and the frontal area of the projectile. Quite simply, it is the hole permanently inflicted via passage of the bullet.
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Temporary cavity - Measures the expansion of the permanent cavity by stretching due to the transfer of kinetic energy during the projectile’s passage. True to its name, a temporary cavity is removed upon the contraction of surrounding soft tissue.
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Fragmentation - Describes projectile pieces (and possibly fragments of bone) which are impelled outward from the permanent cavity. Such fragments may gouge muscle tissues, blood vessels, etc., apart from the permanent cavity. Fragmentation is not necessarily present in every projectile wound. It may or may not occur, and can be considered a secondary effect.
Projectiles incapacitate by damaging or destroying the central nervous system, or by causing significant (and potentially lethal) blood loss. In no uncertain terms: the more damage a bullet inflicts, the greater the likelihood that it will incapacitate its target.
Wounding Factors by Common Calibers
The effectiveness of a bullet depends heavily on shot placement and four additional factors. While none of them has a direct bearing on incapacitation, they must all be considered.
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Shot Placement - Where the shot strikes the body matters greatly. A bullet’s potential to wound depends heavily on the amount of soft tissue it bores through, or whether it encounters bone.
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Bullet Design - The bullet’s design affects how it reacts with a target during and after impact. FMJs typically conserve their shape, whereas JHPs expand to gouge wider wound channels into their targets.
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Velocity - When two bullets of the same weight strike a target, the one traveling at the higher velocity will necessarily transfer more kinetic energy to said target. The faster-flying bullet’s potential to wound is accordingly greater.
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Penetration - The distance a bullet travels upon striking its target has a material effect on its capability. Shallow penetration is less likely to reach a vital organ. Conversely, a bullet that passes clean through its target may inflict inadequate damage to incapacitate it quickly.
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Caliber - A bullet’s diameter directly bears on how wide a wound channel it can inflict. Generally speaking, the wider the bullet, the wider the hole it bores through its target.
Disclaimer: Bullets of the same diameter are seldom interchangeable. Weight, velocity on impact, frontal profile, sectional density (i.e. capacity for penetration), and terminal ballistics (i.e. capacity for expansion/tumbling) all have a material effect on a bullet’s ability to incapacitate its target.
10mm Bullet Wound
A 10mm Auto bullet is 0.4005" in diameter (i.e. slightly narrower than a Crayola Super Tip marker). Although the width of the entry wound will be proportional to the diameter of the bullet, the exit wound varies depending on impact velocity, bullet design, and shot placement.
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Entry Wound (FMJ): Similar to the diameter of the bullet.
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Exit Wound (FMJ): Slightly larger than the entry wound.
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Entry Wound (JHP): Similar to the bullet’s diameter.
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Exit Wound (JHP): Significantly larger if expansion successfully occurs; may be approximately the diameter of a penny (0.74" to 0.79").
.40 S&W Bullet Wound
.40 S&W bullets are 0.4005" in diameter (i.e. slightly narrower than a Crayola Super Tip marker). Although the width of the entry wound will be proportional to the diameter of the bullet, the exit wound varies depending on impact velocity, bullet design, and shot placement.
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Entry Wound (FMJ): Similar to the diameter of the bullet.
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Exit Wound (FMJ): Slightly larger than the entry wound.
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Entry Wound (JHP): Similar to the bullet’s diameter.
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Exit Wound (JHP): Significantly larger if expansion successfully occurs; may be approximately the diameter of a penny (0.74" to 0.79").
9mm Bullet Wound
A 9mm bullet measures 0.355" in diameter, slightly greater than the diameter of a pencil (0.275"). The size of the entry wound is proportional to the size of the bullet. The exit wound varies depending on impact velocity, bullet design, and shot placement.
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Entry Wound (FMJ): Similar to the diameter of the bullet.
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Exit Wound (FMJ): Slightly larger than the bullet’s diameter.
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Entry Wound (JHP): Similar to the bullet’s diameter.
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Exit Wound (JHP): Larger than the bullet’s diameter; potentially as wide as 0.50".
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