Is Bullet Design More Important Than Velocity For Self-Defense Ammunition?

self defense ammunition
When picking self-defense ammunition, what’s the prime attribute to look for? A lot of people would tell you it’s velocity, and with the popularity of +P ammunition as carry ammo for both police and civilian carriers it would appear to be a good one.

Or is it bullet design? There are design attributes of expanding ammunition.

Why Do Hollow Points And Other Types Of Self-Defense Ammunition Expand?


When it comes to self-defense ammunition, the jacketed hollowpoint is the reigning king of the day. In times past, the lead semi-wadcutter hollow point and the soft cast lead bullet before that were the dominant rounds of the day. Each is known for expanding when they enter soft tissue, causing both a larger wound cavity to form but also slowing to a stop inside the target.

How does this work?

When the bullet enters a soft-tissue target, the pressure on the front of the bullet increases dramatically. Since a jacketed hollow point has an exposed core, more pressure is exerted on the rim at the tip of the bullet because that’s the part that hits first. The lead core peels outward, deforming the jacket and causing the trademark “mushrooming” of expanding ammunition.

Previous forms of carry ammunition like the LSWCHP and soft-lead bullets of the 19th century would likewise deform, though they didn’t necessarily mushroom as dramatically as quality JHP ammunition of the present day.

So, it is therefore the case that the desired performance of defensive ammunition is produced by the hydraulic pressure of soft tissues. However, as anyone that’s done much ammo testing or looked at ammunition tests knows, not every hollowpoint actually expands when it hits a target.

What Affects Expansion?


The mechanism by which expansion happens is hydraulic pressure. What affects how it acts on the bullet when it enters the target?

First is velocity. If a bullet doesn’t work at a slower velocity, making it go even faster can make it work or make it work better, which is why +P ammunition became so popular. After all, barely anything happens to your bumper if you run into a bollard at 5 mph or less. Ram into the same bollard at 50 mph and your car will be totaled.

However, the other aspect is design of the bullet itself, in terms of materials, construction, and geometry. Arguably, it’s more important.

Frontal surface area is crucial. You see, for the hydraulic pressure to work on a bullet and produce expansion, there has to a good amount of real estate for it to push on, which causes the core to peel back rather than continuing through the material. This is why “wide mouth” hollowpoints expand more reliably than narrow hollow points.

Metallurgy is important in this respect; the softer the lead core, the more easily it will expand. The harder the jacket, the less easily it will be peeled back.

This is also why .45 ACP JHP rounds (the “flying ashtrays”) are thought to expand more reliably than 9mm hollowpoints. This was certainly the case for many years, though modern 9mm hollowpoints, even standard pressure rounds, are now no worse than their larger counterparts.

Other aspects of construction also make, pardon the pun, an impact. For instance, a reverse taper – where the jacket is thicker at the tip than the base – combined with a cut in the jacket can result in drastic expansion under pressure. Posts in the core of the bullet or polymer inserts can also aid in expansion.

Bonded bullets, which attach the jacket to the core by one of a number of methods, prevents separation or fragmentation. Provided otherwise good bullet design, expansion is controlled and reliable. This has made bonded ammunition very popular in both defense and hunting applications.

In short, velocity helps as a higher velocity impact will amplify the force of the impact, but a good bullet will expand at almost any velocity, let alone at high velocity for caliber – so you don’t necessarily need a +P or +P+ round for it to perform reliably at the moment of truth. That said, if your carry gun feeds +P rounds well and you shoot your preferred overpressure ammunition well, by all means keep carrying it.

  • Bdpenn

    Well done article. All the factors brought forward to explain the end result. Thanks.

  • “In short, velocity helps as a higher velocity impact will amplify the force of the impact, but a good bullet will expand at almost any velocity, let alone at high velocity for caliber – so you don’t necessarily need a +P or +P+ round for it to perform reliably at the moment of truth.”

    It all depends. Bullets designed to expand at 800-1000fps will fragment at 1100fps. There are a lot of you Tube channels where this stuff is tested. Loads of Bacon channel has done a lot with this and his cast lead hollowpoints do about as well as some jacketed hollowpoints, YMMV. If a bullet is designed to expand at a higher velocity for a given cartridge and that velocity range is attained, chances are that the higher velocity cartridge will be more effective than the lower velocity one, given similar expansion. Golddots expand well at low velocities and speer tends to load them light. Comparing that to a Federal HST +P or Winchester Ranger T +P (We’re talking 45acp here), I’d rather have the latter. Look at the tests Lucky Gunner did. They are pretty extensive. Brassfetcher does some good testing as well. Bullets have come a long way in the last 10 years and that’s a good thing, but all things being equal, I’d rather use the cartridge with the most energy that expands well and that I shoot well.

    Of course we could also go back to a 255g 45 Colt @1000fps. That works too.

  • J.W. (Jon) Hood

    For my “2-Cents worth”, I don’t find any discussion of high velocity, JHP’s or HP’s of any variety, involving over-penetration. The object of a personal protection round would be to stop the aggression or situation. The higher the velocity, the more penetration would be the case.
    Involved would be the over penetration, which would include people and objects not intended to be involved. In my opinion a lower velocity projectile designed for maximum expansion, at this velocity, would be preferable. The stopping power of any marginally acceptable caliber, should be acceptable at a lower velocity to stop a situation without “over-carry” to the adjoining and close proximity of others. Plus, if properly designed the rounds could provide proper expansion, at a lower velocity, without over-penetration and passing through, walls, vehicles or other obstructions and involving other concerns.
    That’s my “2-cents worth” and I thank you for allowing me to express it. Remember, it’s not the size of the dog in the fight, it’s the size of the fight in the dog.
    Best regards, to all and stay safe,
    J.W. Hood
    USCCA – 336096

  • Mikial

    A FMJ round at a high velocity will punch a clean little hole that does not hit a vital organ will do far less damage than a lower velocity HP round that hits the same spot. It’s as simple as that. The damage a bullet does depends on the shock it delivers to the soft organs of the body, unless it hits a vital spot like the heart or the spinal column. The best is a combination of a high velocity round that is an HP expandable projectile.

    • You’re kidding, right? Not hit a vital organ? Have you seen what a 5.56 does? The 45acp ball has killed plenty people. That said, On humans, a hollow point is preferred and if that isn’t possible, I’d use a lead SWC in a large caliber bullet. Ask elmer keith how it worked.

  • Iowa10

    I thought you were going to compare to FMJ rounds.

  • Maudlean Spires

    Lucky Gunner did a lot of tests on ammo. They fired five rounds into ballistic jel. They measured the penetration, size of the bullet expanded, the weight of the bullet after it was fired and took pictures of the five rounds of each one tested. These tests and pictures can be looked at by going to Lucky Gunner Ballistic charts website. They tested several different calibers and also compared the results for you to see as well as the pictures of the mushroomed bullets. It was very interesting to see the pictures of the bullets after they were fired. I was of the impression that faster moving rounds would do a better job of expanding but some of the results of their tests proved to be the opposite. A heavier bullet that moved slower actually expanded more dependably. Some of the name brand ammo also didn’t fare as well as expected. You can see the results and compare the different calibers in the same brand of ammo.

    • I was impressed with the Winchester Ranger T +P and Federal HST +P in 45acp. The expansion/velocity/energy was very good. Some of the best tests are prom Brass Fetcher. They calculate energy transfer over penetration. Really interesting stuff.

      • Maudlean Spires

        The pictures of the bullets after they were extracted were what told me a lot about some of the ammo. Some of the rounds didn’t expand at all. The critical defense Hornsby rounds with the filler in the hollow point showed that it helped a lot about keeping the denim from clogging The holes. This allowed them to do a better job of expansion.

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