The Best Self-Defense Caliber: Ballistics, Informed Opinions, and Conclusions

2022-07-23 23:23:59 By : Ms. Sara Zhao

As if lives depend on it, everyone has a subjective and biased opinion about the best self-defense caliber for deadly-force situations. Well, everyone is absolutely correct. This is not something to be taken lightly, and the debate has been going on for many years. But, I want to shed some light on the ten caliber factors I believe are very important, based on ballistics research data, objective documentation, and knowledgeable comments from several experienced, well-informed handgun shooting authorities and some friends. I welcome their salient and professional statements as strong input. I’ll list just some of their individual comments and opinions below and then draw my own conclusions like you might want to do as well. So, the caliber decision will be more open to a lot of input, scientific, rational, and objective, and not so interpretive, emotional, and subjective. At least this will be a somewhat structured thought process, with the sincere goal of helping you and myself make an informed, very-important decision about this so critical caliber matter.

Caliber is the inside diameter measurement of the barrel of your handgun. It matches the diameter of the bullet projectile portion of the ammunition cartridge. A 9mm caliber gun has a barrel with a .356-inch barrel diameter and uses 9mm rounds with the same diameter, for example. A .45 ACP caliber gun, on the other hand, has a barrel with a .452-inch barrel diameter and uses rounds with that same diameter. Caliber is measured primarily in fractions of an inch with a few calibers measured in millimeters, like the 9mm. While there are exceptions with handgun calibers, usually the smaller the diameter, the smaller the round, and the smaller the bullet hole in the attacker. So choosing the optimal caliber for your self-defense means that you must consider both the characteristics of the gun and those of the ammunition, as well as several other factors, which I will give below.

Also, it is important to understand how caliber applies to stopping an attacker when selecting your self-defense handgun and ammunition combination. Of course, defenders want the best handgun with the best ammunition to effectively stop an attacker. Accuracy is a key factor, and serious training and practice are required to acquire the ability to hit where you need to hit in the stress of an attack. The caliber you select is a primary factor regarding equipment selection and your overall success.

Bullet penetration is one of the primary factors, if not the primary factor, in deciding which handgun caliber to choose. This is the amount of human tissue the bullet can pass through. These include fat, muscles, bones, and organs. Generally, large and heavy-grained bullets have superior penetrating power. They inflict massive tissue damage and are very optimal to stop the target in its tracks. The F.B.I has determined that a bullet must penetrate to a depth of at least 12 inches, as tested using 10% calibrated ordnance gelatin. 15 inches penetration is considered optimal and 18 inches is maximum for inflicting a reliably incapacitating wound. Ideally, bullets should remain inside the target and excessive penetration can increase the risk of collateral damage.

Over-penetration is an extremely important factor to consider. Where the bullet travels after you fire it is of the utmost importance, especially if you live in an apartment with a family and children or near others. If you miss your shot, or it passes through the attacker, it may place neighbors or others in adjoining rooms in danger. What is your home or apartment constructed of? Is it brick or drywall? This might affect the defensive caliber and rounds you load. Does the bullet stop, or does it pass through the wall or the attacker? Knowing your layout and where the best place to engage the attacker is important. If you are outside of your home, you may have innocent bystanders near the attacker. Knowing what lies behind your target is your responsibility.

The Permanent Wound Cavity is the size of the hole and the volume of soft tissue permanently crushed and destroyed by passage of the bullet in the body. The diameter and surface area of the bullet directly impacts the size of the permanent cavity. The caliber, shape, and composition of the bullet are important in creating a Permanent Wound Cavity. Every bullet can leave behind a permanent cavity, which is measurable. Generally, the bigger the Permanent Wound Cavity or hole, the better is the stopping power.

The Temporary Wound Cavity is created when the bullet transfers kinetic energy to the surrounding tissues, causing them to extend and stretch outward from the wound track. Damage to tissues depends on their elasticity limits and the Temporary Wound Cavity created. The liver and spleen, for example, are inelastic and fluid-filled organs which are very susceptible to damage. Muscles, skin,  and lung tissues are more resistant. If a bullet expands, its kinetic energy transfer will increase, which increases the volume of the Temporary Wound Cavity. So, temporary cavitation exists more in high velocity and high energy projectiles, like in rifles and shotguns. Generally, the Temporary Wound Cavity is not a reliable wounding factor in low-energy handgun bullets.

Very generally, Kinetic Energy is the bullet’s energy coming from the handgun’s muzzle when the gun is shot. It is caused by motion and acceleration and the Kinetic Energy of the bullet is maintained until a change in velocity occurs. So, a bullet’s Kinetic Energy lessens during flight and, generally, a bullet with a heavier grain weight moves faster. A bullet with a stronger muzzle Kinetic Energy can often inflict more body tissue damage. Of course, bullet performance is affected by its weight, type, design, Muzzle Energy, Muzzle Velocity, and distance. Recognize that handgun calibers do not generally have enough Kinetic Energy transferred to the surrounding tissue.

Fragmentation refers to the bullet pieces or secondary bone fragments which are impelled outward from the Permanent Wound Cavity, which may severe muscle tissues or blood vessels. Since most modern, premium handgun bullets use bonded projectiles, like copper-jacket bonded or lead core, Bullet Fragmentation is very low and inconsequential in handguns. Bullet velocity and design are two important factors that determine fragmentation. Of course, fragmenting bullets will not over-penetrate. Both mass (bullet and hole size) and velocity contribute to the energy and damage of the bullet. But, the bullet velocity is a more important determinant of tissue damage because if the velocity is doubled, the energy increase four times.

Bullet expansion is a key property of self-defense calibers, since as the projectile flattens upon impact, it causes more damages inside the attacker’s body. As the bullet expands, a larger wound cavity is created and more energy is transferred for quicker damages to tissues and organs… to stop the threat, not necessarily to “kill.” Upon impact, a hollow point bullet is designed to expand, deform, and mushroom resulting in greater internal damage. However, some do not live up to what they were designed to do, so choose your self-defense ammo very carefully.

Keep in mind that hollow point rounds, generally, have a better rate of expansion and typically penetrate less than full metal jacket rounds and those that do not successfully expand. A commonly-used measurement is to have an expanded diameter of at least 1.5 times the original diameter. This usually results in an adequate expansion amount for any caliber, resulting in a larger hole size and wound cavity.

It makes sense to pick the heaviest hollow-point bullet that reliably expands to the widest diameter, while still penetrating between 12″ and 18. Some hollow point rounds will not expand and become plugged with clothing or other debris, thus acting like a usual ball, full-metal-jacket round.

Another important factor is that Bullet Expansion contributes to limiting the chances that the bullet will go through the attacker and hit or injure an innocent person. Expansion slows the velocity of the round and prevents over-penetration. Here are some typical 9mm bullet expansion diameters.

Muzzle Velocity is the speed of a projectile, bullet, or shell leaving from the muzzle at the very moment it leaves the end of a handgun’s barrel. Velocity is usually highest when leaving the muzzle and drops off steadily due to air resistance. Bullets traveling less than the speed of sound (about 1,100 ft/sec) are considered to have subsonic Velocity. Speed or Velocity depends on air temperature, humidity, wind speed, and barometric pressure.

Selecting the right type of ammunition for your self-defense handgun is an important decision. Certainly, having the proper ammunition is necessary for your handgun to perform effectively and to keep you safe. Obviously, the recoil generated by the gun, felt by your hand, wrist, and arm is primarily determined by the ammunition and its caliber you shoot through the handgun. Ammo factors like the weight and size of bullet, cartridge type, and the powder charge determine  recoil, amount of energy produced, and overall performance. Since recoil is finally determined by the forward movement of mass, it is directly influenced by the mass and velocity of the bullet and by the mass and velocity of the powder charge. While a standard full-metal-jacket round will often be the best option for regular training and practice, the defender should also regularly shoot jacketed-hollow-point rounds to confirm how their chosen self-defense caliber, handgun, and ammo type are cycled and handled with their particular gun.

Common bullet weights for 9mm include 115gr, 124gr, 125gr, 147gr, 158gr, and 165 gr. Generally, heavier weight/grain bullets, like 158, 147, and 124 grain hit harder, have more recoil, and are more expensive than 115 grain, for example. Most defenders practice and train with 115gr ammo, and carry heavier loads for personal defense. Extra-heavy bullet weights can knock down steel targets, are subsonic, have deep penetration, are often used in suppressed guns, and are used in certain competitions, like Bianchi Cup, IPSC, and  IDPA. Here are some types of cartridges you might want to explore on your own.

Ammo designated as +P or +P+ is over-pressure handgun ammo that has been loaded to produce a higher internal pressure when fired than does standard ammo of its caliber, given by SAAMI and NATO specifications, but less than the pressures generated by a proof round. They have a bit more pressure and extra gunpowder, but still are within industry standards. These rounds provide more energy to reliably get an expanded bullet deep enough to do its job. Note that some handguns are designed for standard pressure ammunition only and should not be fed the +P and +P+ ammo. Usually these high-pressure rounds generate more felt recoil and are harder to control than standard ammunition, due to the lack of space to expand which creates extra pressure. Generally, these high-pressure loads give you more energy, more speed, and more stopping power. The latter is up for debate, of course. And this type of ammo does not give significantly consistent energy, speed, or stopping power. So is it worth the extra money for the extra pressure rounds? These rounds vary significantly, so your call!

Here is my Summary about the performance of heavy and light grain bullets for self defense.

(Note: A large, heavy-framed handgun might help absorb some of the recoil, reducing “felt” recoil for some. Also, propellant burn rate can also affect recoil.)

See my article about selecting Heavy or Light Bullets for Self Defense.

Heavy or Light Bullet Grains for Self-Defense? Considerations and Recommendations

As handgun barrel length gets longer, you can expect better handling, better muzzle control, less muzzle flip, enhanced sighting, and generally better terminal ballistics. So what specifically are the affects of barrel length on terminal ballistics, including accuracy? Well, there are different opinions about this. Some say that barrel length has nothing to do with accuracy in handguns. Believing that accuracy is not directly proportional to handgun barrel length. So that a difference of an inch or so in barrel length has no noticeable impact on inherent accuracy.

While velocity is related to barrel length, most say that accuracy is not. For example, the accuracy from a two-inch J frame revolver is generally as good as that from a three-inch revolver barrel. However, longer handgun barrels do increase the length of the sight radius plane, permitting more precise aiming when sighting. Since the sight radius is longer on the three-inch, most can shoot the three-inch better. But short-barreled pocket handguns do not allow for a complete powder burn, making the velocity less. So, the short sight radius of a short-barreled pocket gun does not enhance accuracy and makes it more challenging to shoot best.

While longer barrels generate higher velocity because the propellant burns more completely, there are diminishing returns with extra-long barrels, depending on caliber, cartridge, and propellant. Longer barrels give the propellant force more time to work on propelling the bullet and extend the time interval where chamber pressure acts on the bullet’s mass. Very generally, a shooter can expect a velocity change of about 20 to 25 fps per inch of barrel loss. Longer barrels help bullets stay supersonic longer and may maintain accuracy instead of dropping over a longer distance. Generally!

While some believe that longer barrels might help just a little with accuracy, of course, these guns are less concealable than short-barreled handguns. Again, longer barrels do not automatically mean better accuracy. And short barrels provide greater concealability, but at the cost of velocity, range, accuracy, and terminal performance. In short barrels, the expansion will usually be inconsistent and unreliable in soft tissue, limiting the bullet’s terminal performance.

Learning to handle and master the recoil of your handgun is the only way to effectively use higher-caliber handguns and ammunition. It is not only about comfort when shooting, but about getting back on target quickly for more hits to stop the threat.

In class after class, we see inexperienced students who cannot handle felt and actual recoil, continuously flinch, and do not follow the fundamentals of effective shooting. We even use no/low recoil .22LR rounds for our students to qualify at the range. Of course, caliber is directly related to recoil management. Proper grip and stance are two of the most basic fundamentals to help control recoil management. It is so important for the shooter to grip the gun properly with a firm grip, to focus on minimizing movement every way the shooter can (cannot totally eliminate movement), and use a handgun that fits the individual’s physical features and hand size. Shooters need to develop the confidence to aggressively lean forward on the ball of their foot and push into the shot, putting most of their weight on their front leg as the shot breaks. Do not shift weight backwards onto the heel. Leaning forward slightly will really lessen recoil.

Shooters must recognize that a lighter handgun will increase felt and actual recoil. Let me repeat that, since many new shooters overlook this. A lighter handgun will increase felt and actual recoil! Recoil movement does not enhance accuracy. So smaller and lighter is not always better for survivability, but does help with concealing the gun. Added handgun weight may make it somewhat more difficult to hold the gun for some, but a light gun will definitely increase felt recoil. Handgun weight has a direct affect on both recoil velocity and recoil energy and is a significant concern for the shooter’s felt recoil. Adding just half-pound muzzle break to a two-pound pistol, for example, will reduce the recoil energy by 20% due to solely the added weight. New shooters eventually recognize that the heavier weight difference is one of the reasons that physically larger guns are easier and more pleasant to shoot.

Marksmanship skills, shot placement, training, and practice matter more than type of handgun, equipment, and caliber used. Your self-defense goal should be to place as many proper hits on target as you can within a very quick time. You must make the caliber and handgun work optimally for yourself. Of course, you must also obtain and use the best equipment for yourself.

Dr. Peter Rhee et al from the University of Arizona, Division of Trauma Surgery, says that most experienced trauma surgeons will testify that what part of the body is hit by the bullet is more important than the caliber and size of the bullet, in a2016 study. That handgun caliber probably does not matter. Dr. Rhee says that a smaller bullet and caliber can deliver more precision and accuracy, but that trauma specialists found that fatal or exiting gunshot wounds were misinterpreted 52% of the time. So it seems that you cannot tell the difference between calibers when a bullet enters the body. Evidence shows that no commonly-used handgun caliber round has the power to cause an immediate cessation of hostile actions, unless the central nervous system is interrupted. What matters most is what the bullet hits when it enters the body. Shot placement is “king.”

So carry a handgun with you, know the fundamentals of shooting, then train and practice to shoot the gun you prefer quickly and accurately. Keep shooting until the threat stops.

Which caliber is best for your self-defense? A handgun of any caliber is better than none. For many reasons, smaller calibers, like the .32 ACP, .25 ACP, .22LR, and .380 ACP, can be handled more easily and controlled more effectively. But, smaller handgun calibers are usually not recommended for self-defense use, as the bullet size and energy are considered too small to inflict enough damage to stop an attacker quickly enough. Their muzzle energies are usually less than about 200 foot-pounds. While a 9mm caliber round has muzzle energies of almost double to near 400 foot-pounds of energy. I like the 9mm caliber for my self-defense. Because the damage inflicted is less traumatic, especially when used against a larger attacker or one that is under the influence of drugs or alcohol, small caliber bullets can have little or no real stopping power. There are exceptions. If you choose a smaller caliber handgun for your self-defense, you must practice often to be as accurate as possible in a life-threatening situation. When using a small caliber handgun, you must rely on your ability to get off multiple shots that hit critical target areas in order to stop the assailant quickly.

Guns and ammunition are tools. This equipment is only as good as the skills you have as the user of the tools. Whatever handgun caliber you use, it is your ability as a shooter that will make it effective.

Train and Practice, Practice, and Practice with your chosen caliber!

* This personal opinion article is meant for general information & educational purposes only and the author strongly recommends that you seek counsel from an attorney for legal advice and your own personal certified weapons trainer for proper guidance about shooting & using YOUR firearms, self-defense and concealed carry. It should not be relied upon as accurate for all shooters & the author assumes no responsibility for anyone’s use of the information and shall not be liable for any improper or incorrect use of the information or any damages or injuries incurred whatsoever.

© 2022 Col Benjamin Findley. All Rights Reserved. This article may not be reprinted or reproduced in whole or in part by mechanical means, photocopying, electronic reproduction, scanning, or any other means without prior written permission. For copyright information, contact Col Ben Findley at

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"Col Ben" is retired with 30 years service in the U.S. Air Force, with joint services Special Ops duty and training, and is Air Force qualified as "Expert" in small arms. He is a Vietnam-era Veteran. Ben is an experienced NRA-Certified Pistol Instructor, NRA Range Safety Officer, and FL Concealed Carry License Instructor. Ben recently wrote the book "Concealed Carry and Handgun Essentials for Personal Protection" (second printing) with 57 comprehensive Chapters about concealed carry and handgun principles, techniques, and tips for both experienced and new shooters. His reference book is endorsed by several organizations and is available on his website at Contact him at

Penetration is probably the best factor for stops, but expansion and permanent wound hole size are also important. Thanks for making me think about this and for reassuring me about my 9mm caliber choice.

Shot placement and the shooter’s accuracy skills plus the handgun being used are major things to stop the threat. There is no magic bullet like you said. For me 9mm is the best caliber, with sufficient energy to get the job done.

Very good summary of many considerations. I like a longer barrel. No 3″ barrels for me. Want 4 inch barrel and shoot 9mm. Thanks.