3 Criteria for Effective Self-Defense Ammo

How Many Bullets Should You CarryThe importance of purchasing good self-defense ammunition for your everyday carry (EDC) handgun, or your home defense gun, is often overlooked. But what does it mean to say you should buy “good self-defense ammunition?”

Your ammunition should do three things consistently. Your self-defense ammunition should:

  1. Reliably feed in your specific gun.
  2. Consistently penetrate between 12″ – 18″ in ballistic gelatin
  3. The projectiles must fully expand, consistently

Let's take a look at each one more in-depth below.


If there is one thing that I'd consider being the most important, it's that the ammunition must cycle reliably in your gun, to begin with.

Expansion and penetration won't matter if your gun doesn't work with your chosen self-defense ammo. So, that is the most important one.

You also need to reliably and consistently hit your target with your chosen ammunition. If you can't, then you need to figure something out.

We always recommend that you run a few boxes of your chosen self-defense ammunition through your gun to make sure they cycle correctly.


bullet over penetration

Penetration is second because, even if the gun cycles properly, if the projectiles don't penetrate far enough into it, they may not do enough damage to stop the attacker. Therefore, you should choose self-defense ammunition that consistently penetrates between 12″ and 18″ when shot into ballistic gelatin. Keep in mind that ballistic gelatin is not the same consistency as human tissue. So 12-14″ on penetration in ballistic gelatin does not equal 12-18″ of penetration in a human body.

However, projectiles must penetrate deep enough to impact organs that cause the body to function normally. When this point is brought up, some will assume then that hollow point, self-defense ammunition, is designed to be “more lethal.” This isn't the case. Bullets are inherently lethal when they penetrate the body at hundreds of feet per second. Even so, not all projectiles are created equal, and some do not consistently penetrate deep enough to start incapacitation immediately. The point is to stop the threat as soon as possible and with the fewest rounds fired.

This is safer for the person defending themselves and the public, as each round fired could potentially miss the intended target and strike an innocent bystander.

We also do not want projectiles that over-penetrate. Bullets that pass through the intended target and strike unintended people are a problem. We will touch on this point again when we talk about expansion.

Many police agencies weigh penetration as an essential characteristic for their duty ammunition. This is because officers are more likely to shoot through barriers like auto glass and body panels than citizen defenders.

FMJ (full metal jacket, i.e., not hollow point) ammo tends to over-penetrate, which is one of the reasons why we always recommend using hollow points (JHP).


expanding hollow-point ammo

First, expansion is important because the projectile flattens as it impacts the threat. When the bullet expands inside an attacker's body, it causes a more significant wound tract and transfers more energy creating cavitation to the surrounding tissues. As a result, the round is likely to impact body functions more quickly and stop the attacker from continuing.

I mentioned this above in the penetration section.

When we talk about ending the threat, we are absolutely NOT talking about killing them.

The phrase “ending the threat” means EXACTLY what the simple definition of those words means. In other words, to stop the person from continuing to do whatever deadly threat action they were committing against the one using defensive force. This post explains a bit more about the difference.

Additionally,  expansion also helps limit the possibility that your bullet will pass through the bad guy and hit someone or something else (known as over penetration mentioned earlier).

Some manufacturers sell ammo that is supposed to expand but doesn't always actually do its job?

I recommend looking at penetration and expansion tests like what Lucky Gunner has done in their lab. They've shot many of the different types of popular ammunition into blocks of gel to see how far each bullet penetrates and expands.

The results may surprise you.

Some popular stalwarts have failed to expand or over and under penetrate in the testing constantly.

So how much expanding should a bullet do? Please don't get too concerned over the exact numbers; instead, choose a bullet that does it consistently. But for you who like numbers, a good rule of thumb is 1.5X its original diameter. But as far as I know, there is no standard. I've also read 1.7X and a few other arbitrary numbers.

For me, in a typical 35 caliber bullet, like 9mm, I like to see the bullet get to at least .5″ in diameter, preferably bigger.

self-defense ammunition

Put it all together:

Put it all together, and you can find ammunition that will cycle reliably in your chosen self-defense gun. And a projectile whose penetration is constantly between 12-14″ when tested in ballistic gelatin.

Let's hear about the ammunition you choose to use in your EDC and why you carry that specific type. Leave a comment.

Also, if you're interested in solidifying foundation firearm shooting principles, check out this course called Shooting Fundamentals. It is a fantastic course for new shooters and those wanting to clean up some bad habits or consistency issues.

shooting fundamentals

About Matthew Maruster

I follow my Lord and Saviour Jesus Christ who is the eternal co-equal Son of God. I currently live in Columbus, Ohio with my wife and daughter. I served in the Marine Corps Infantry. I was a Staff Sergeant and served as a Platoon Sergeant during combat in Iraq. After I was a police officer at a municipal agency in San Diego County. I have a Bachelors's Degree in Criminal Justice from National University. MJ Maruster Defense.


  1. Mark Linebarger on January 4, 2021 at 5:26 am

    Anytime you make an ammo change, you need to verify they will run thru your firearm. Eg; some semi autos don’t like a lot of exposed lead on a jhp…and some of the new defense stuff with the splits/laps in the jacket are creating feed problems in some firearms
    All this speaks to your first criteria.

  2. V on January 4, 2021 at 12:03 pm

    I did carry hollow points but had 2 where the nose went back into the round, ie, the round was shortened so it dropped down so it wasn’t in the chamber. 2 rounds had to be extracted manually. I’ve since switched back to practice rounds to carry–not my preferred choice. At home, I practice with standard rounds, and as for now, still use them when cc. Not my preferred choice. With the lack of ammo available, people can’t practice to be proficient, so what are we supposed to do. Responsible firearm owners want to be able to defend ourselves and innocents and NOT risk bystanders…

  3. Mitch on January 4, 2021 at 1:00 pm

    Shoot that horse? Really.
    What of its family?

  4. Mitch on January 4, 2021 at 1:23 pm

    Though I appreciate the “wound” part, i am neither a horse or alone in this.

  5. Zach on January 4, 2021 at 9:28 pm

    What is “…typical 35 caliber bullet…”??

  6. David Tyree on January 5, 2021 at 9:47 am

    I only wish I could get the ammo I want. Right now you have to gram whatever you can get. In the old days, yes, I would use one allowable brand of ammo. Not available now.

  7. Dave on September 27, 2021 at 11:27 am

    Using Winchester USA Ready 124 gr. + 9mm. It functions all the time and has some amazing test results that are available online. You can as well check your lot number online for performance numbers as tested.

    It’s accurate and well made ammo. But as with other comments, it’s still not readily available as needed. Hopefully that will change.

    It’s a bit pricey compared to your basic practice ammo but it is worth the extra cost for EDC.

    • nomen nescio on February 11, 2022 at 11:00 am

      TNoutdoors9’s tests show the USA Ready 124gr 9mm bullet overexpanding and underpenetrating, not even hitting 12″ in real gel. Condition Zero tested it in the clear synthetic gel that exaggerates penetration by 25% or more and it still barely hit 12″. Expansion isn’t impressive either, though in every test there is significant weight loss.

      This is the first time I’ve ever seen a 124gr 9mm hollowpoint fail to get to 12″. Reliable expansion is normally the problem, not adequate penetration. I think I will stick with Ranger-T, Gold Dot, or HST, thank you very much. Even 30+ year old Hydra-Shoks and XTPs are superior performers. Winchester got this one wrong.

  8. Martin on September 30, 2021 at 9:16 am

    Critical Defense or Hydroshock depending on the gun & 2 reloads

  9. Tony on September 30, 2021 at 3:10 pm

    I believe Federal HST and Speer Gold Dot are the most popular/recommended self-defense ammo among quality shooters/instructors as well as police departments. A little surprised those two didn’t get any mention. I carry Federal HST.

  10. Jeff Walters on October 24, 2021 at 2:06 am

    Well, the FBI uses Winchester PDX1 bonded jhp ammo. So that’s good enough for me. I would really love to run a lot of it through my Springfield Range Officer’s 1911 .45 target pistol, but at damn near $2.00 a round, I can’t really afford it. I’m probably going to shoot a bunch of Armscor fmj (at 52¢ per round) to get the feel of the gun, and then cycle 4 or 5 magazines of the PDX1 through it and call it a day. It’s not the ideal test of how well the gun will function with that ammo, but I can’t afford to shoot 200 rounds at that price.

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