The Curious Case Of The Over-Penetrating Round

Feature | Ammo in wooden tree | The Curious Case of the Over-Penetrating Round

Read the dangers of an over-penetrating round and the steps you can take to minimize or prevent further damage.

RELATED: Owning A Gun Safely At Home

In this Article:

  1. Over Penetrate Definition
  2. The Issues Surrounding 9mm Overpenetration
  3. Should You Give Up On Your 9mm and the Over-Penetrating Round?
  4. You Can Do Better

Over-Penetrating Round | How Dangerous Is a 9mm Overpenetration?

Over Penetrate Definition

Gun and ammo in the table | The Curious Case of the Over-Penetrating Round

The 9mm over-penetrating round had come a long way since its introduction back in 1902. The vast array of ammo makers, grain-size bullets, and designs make this the go-to round for many.

There is one problem, however. The 9X19 cartridge or 9mm over-penetrates much farther than one hopes.

The home defense ammo may maim an attacker, but it can also put innocent bystanders in danger.

To help you understand the possible danger of over-penetration, let’s define it.

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Over-penetration occurs when the bullets go through walls and flesh farther than other self-defense projectiles.

In general, bullets are either hollow point or full metal jacket. The latter refers to a round tip, ball, target ammunition.

What Is a Hollow Point? It is ammunition with a hole at the tip. Its purpose is to slow down the journey of the bullet and expand itself once it hits a barrier such as a wall or flesh. In principle, it is less deadly, so some experts recommend it for home defense use.

It’s the one that tends to travel farther. This fast-moving bullet is narrow enough that it takes a while to slow down in a body, wall, or car.

Jacketed hollow points are also famous for traveling through walls. They do not expand when they hit something hard.

The Issues Surrounding 9mm Overpenetration

A lot of people don’t have enough information on what a home defense gun should look like. Some new gun owners feel a 9mm ammo is sufficient for home protection because of what they hear or read.

Of course, the 9mm is great for recoil management. It then allows the shooter to get back onto target quickly.

It does have its issues, though, especially when it is an over-penetrating round. Here’s a scenario.

Let’s say a criminal is stupid enough to attack you with your 9mm handgun in your home. When you are under attack, your body will exhibit a “fight or flight” response.

When this happens, a gun that weighs a few pounds begins to shake in your hands as your vision starts to blur. The result can be several missed shots.

You are more likely then to fire in the direction of your kids before you can connect a bullet to your attacker.

That’s not all. If it’s an over-penetrating round, there’s a chance you can injure the attacker, but the bullet exits. It may then hit another person such as your child.

RELATED: Weapons Retention During Close Quarters Gun Fighting


The 99mm handgun remains an excellent concealed-carry firearm or a home defense weapon. It doesn’t mean you can shrug off the possibility of having an over-penetrating round.

Remember, it has the potential to go through several layers of sheetrock before stopping. It may also tear the flesh of your attacker and your loved ones.

Instead of using a 9mm as a home defense gun, consider other options such as these. Manufacturers had you and your home in their minds when they designed them.

Another choice is a 9mm frangible ammo, which can disintegrate once it hits an object. It, therefore, reduces its over-penetration ability.

You Can Do Better

This isn’t saying you have to run out and sell your 9mm guns or you shouldn’t buy one.

One of the basic rules when it comes to gun use is to never assume anything. Just because the manufacturer says it is not an over-penetrating round doesn’t mean it’s not.

Given the ideal situation, a bullet can go through almost anything and travel farther. If you do decide to keep your 9mm, bullets that don’t go through walls are not the only answer.

Establish a home invasion defense plan. Make sure everyone in the household knows it to avoid accidental shootings.

Educate yourself on handling home defense handguns to ensure no over-penetrating round will hit the wrong target. Train as often as you can to develop muscle memory.

Most of all, never place your finger on the trigger until you are sure your attacker needs to die.


Learn more about an over-penetrating round in this YouTube educational video by Warrior Poet Society:

Can a 9mm go through a person? Yes, it can happen.

Anything that has enough power to do damage to the human body can over-penetrate farther than you want it to.

If you own a 9mm handgun (or any gun, for that matter) as personal protection or home defense, it is essential you understand the definition of an over-penetrating round. Most of all, you should know its impact, so you can reduce the danger that comes with its use.

Do you have any other thoughts about an over-penetrating round? Let us know in the comments section below!

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Editor’s Note: This article was first published in April 2016, and has been updated for quality and relevancy.



13 Responses to :
The Curious Case Of The Over-Penetrating Round

  1. Ed Gleason says:

    I’ve been telling friends this for a long time. About 8 years ago my sister had to defend her self from two intruders late at night, although she missed and they ran the target ball ammo that she had in her gun went through a living room wall and then made it outside.

  2. Tom Krynock says:

    Frangable rounds or shot shells?
    Since I live alone and in the country over penetration is not a big consern to me.
    I have always liked 9s, and have several “handy.””

  3. DEFENDER88 says:

    When shooting practice, matches, etc I use std Ball ammo, cheaper for practice.
    When I put my gun up in the car or house I load a mag(which I keep on hand and pre loaded) of HP’s in it. So I always have fully loaded mags of each on hand. Never know when you might have/”need” to shoot thru a car door or wall.

  4. USCBIKER says:

    .40 SW JHP for me. They tear open a big cavity, have nearly 50% more knockdown power than the 9mm and spread, so they stay in the perp’s body, not other people or your house.

  5. Gary Martin Smith says:

    Scary looking long guns? Really? By the way, 00 buck can overpenetrate sheetrock as well.

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  6. Steve Foster says:

    As the Chief of Police of a police department, my concern of over penetration has been a concern forever. I have found a new .40 caliber bullet that gives you just what you want, knock down without over penetration. OATHAMMO.COM. We have just changed to this ammo and have shoot several hundred rounds using the Generation 4 Glock 40. I can tell you that shooting this bullet thru car doors and windshields that there is no over penetration. It hit the water jug that was set up in the driver seat and stopped there. When fired thru the driver door it did not penetrate the passenger door. If you go to the website you will see the bullet shot into the jell and it is an expandable round that does what is suppose to do: DROP THE TARGET AND ONLY THE TARGET.

  7. biffula says:

    The ‘knockdown’ advantage of 40 cal over 9mm has been proven a myth. Empirical data from actual gunshot victims, not tests shot into ballistic gel, show no advantage of one round over another. My magazines hold more 9mm rounds, there are infinitely more choices of loads and bullet types for 9mm that take away any advantage 40 cal might have had(and that take away the worry of over-penetration), 9mm is cheaper and more readily available, and data also shows 9mm is more accurate in actual combat settings than 40 cal. I’ll stick with my 9mm thank you.

  8. Steven says:

    Thank you Officer Foster! I have 3 good friends that are L.E.O. and I get as much info as I can from them. We have had many conversations about the concern of over penetration. I’ve been shooting for a long time and it’s always like you said, “Forever” been a concern. You have that issue and the hearing damage when a high powered firearm is used in the home. You have convinced me to go from 9mm to .40 and go to OATHAMMO.COM to purchase ammo. I have pied my home many,many times so that I know where my round will end up if I have to use it, which I pray to God I never do. I don’t even like the law that I can shoot someone in my driveway trying to steal my car and refuse to do it. What some people fail to realize is that person is someone’s Son, Father, Brother, Daughter, Sister…well you have the picture. So I’m not being threatened and some dumb 17 year old decides he wants to steal a car. I will yell out the door at him, armed, of course, and dial 911 and let the Police do their job and hopefully nobody dies that night. I’ve had people argue with me that they are low life scum that took the risk of being shot so I’m not letting them take my car when all I have to do is shoot them. In my thinking if they are not a direct threat to my loved ones or myself the shooting just isn’t justified yet people have been acquitted many times for this. I look at the taking of a life very seriously. The way I see it it’s God’s job to determine when a person leaves not mine unless I have no choice. I’m 58, handicapped but have trained marines and a few L.E.O.’s as I’ve held 2 black belts and study Krav Maga and Dim Mak. I fought amatuer years ago and had 13 bouts, won 11, tied 1, and lost 1. I have become a much better Martial Artist since then and am not a believer in all the dancing that are done with Kata’s, and view kickboxing for what it is…a sport. On the street it happens in seconds and it’s real life or death. I always have bear spray in my pocket and put that to work 1st, disable my bad guy and get out of there. If more people would train that way there would be less innocent people being hurt!

  9. Mikial says:

    I’ve honestly lost count of the number of articles I’ve read trying to convince people of why they should or should not use 9mm, and the number of articles and discussions on over penetration. As one of the comments above in the Facebook only section ( I don’t use FB) said, some guns feed more reliably with FMJ, so it’s the only realistic option for self defense loads. My wife’s favorite 1911 that she keeps next the bed is like that. In that case you have to be extra careful of what’s beyond your target. For carry she uses a Beretta 92 with hollow points. My Glock 21s will digest anything I choose to load them with, so HTPs are the standard load.

    Since we live in the country and based on the layout of our home, any round we shoot from the bedroom in self defense has nothing to hit bu a forest outside the house, my Saiga 12 is my first choice unless I can’t get to it fast enough, in which case it is the G21 I always carry. Always.

    In the end, you have to do the best you can with what you have. Practice, train, employ situational awareness, and hit what you’re shooing at.

  10. Diane says:

    On penetration: I was at a friend’s home once and in the living room with his wife and young son. All at once there was a loud bang. The husband was in the bedroom unintentionally fired his .45 pistol. Here was the penetration level: through the bathroom hollow door and into the wall. It did not penetrate further into the next room. The hole in the door was about 6″ in diameter and in the wall it was smaller and not as round. So, it went through the door, past the sheet rock in the wall and did not penetrate the next layer of sheet rock.

    I was talking with a guy who had been in Nam and he told me he had carried a .357. He was charged by an enemy soldier, unloaded all six rounds of .357 into the guy, who kept coming. He was wounded and one of his buddies shot the oncoming soldier with a .45. Blew the enemy’s arm off. The guy told me he borrowed the .45 and shot up his .357.

    Stuff happens and we never know what a round, regardless of caliber, will do. There is a guy walking around with 5 .22 bullets in his head and he is just fine. Another person will be killed by one .22 round to the gut. I will remind you of the shootout with the FBI in Florida where the main bank robber was shot multiple times and kept going. When I was training for CCW, we were shown a reenactment of a situation where two cops came to take a guy in who was so hyped up on some drug it was almost impossible to take him down. He killed one of the cops and the other one managed to shoot him point blank in the side of his chest and he told the cop he got him a good one that time. After multiple hits, it took two shots to the head to finally kill the guy.

  11. Larry Barriner says:

    I plan to buy a handgun soon. What is best way to go about it. Do I need all paperwork filled out, submitted and approved before or do I get the gun sooner?


  12. BH says:

    Do your research. There’s a great gel test comparison on that shows most of the modern ammo in several (.380-.45) rounds. The is data-specific results on with 5 rounds per bullet brand & type showing penetration depths, expansion, velocity , weight retention, permanent vs. temporary wound cavity and averages-as well as comparisons of expansion to other rounds in the same caliber.

    It certainly eliminates some of the guesswork, bravado & speculation that we see on a daily basis. It’s an excellent piece. Pease check it out(no, I have nothing to do with the site), and decide what’s best for your situation. Stay safe
    The site link is below:

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