Bullet Expansion: How & Why

Editor’s Note: The following is a syndicated article by author Tamara Keel that first appeared in USCCA’s Concealed Carry Magazine Volume 15, Issue 2 February/March 2018 under the title, “Expansion: How & Why.” 

“9mm might expand, but a .45 never shrinks!” goes the old saying, but there’s a lot more to the how and why of bullet expansion than can be covered in a bumper-sticker slogan. While it’s true that the expanded bullet makes a larger-diameter hole, that’s actually only a secondary effect to its most useful function: The act of deforming the bullet uses up a large amount of its energy.

Respected trainer Chuck Haggard points out that his department used the 124-grain +P Gold Dot hollow-points and that for years, in shooting after shooting, the spent projectile would be found — fully expanded — in one of three places: just under the skin on the far side of the bad guy, stopped in the clothing on the far side of the bad guy or on the ground about 10 feet past the bad guy.

You literally cannot ask for anything more than that out of a pistol bullet. When moving at pistol velocities, a projectile’s only real wounding mechanism is penetration. There’s no magic shockwave or hydrostatic voodoo or anything like that happening at 1,200 feet per second, let alone 800 or 900. As Tom Givens puts it, these little popguns we carry concealed are nothing but remote-control drills: They put little .355- to .451-inch-wide holes in whatever they hit. How deep those holes end up being has far more bearing on their ability to stop an attacker than any 1/10th-inch difference in diameter.

Being bipedal predators, humans have all the really important parts, like the heart and spinal column, buried deep inside, on the side facing away from their potential prey so as to be shielded from damage. Any handgun round has to be able to reach these vital parts while still retaining enough momentum and energy to damage them. At the same time, the bullet ideally should not retain so much momentum and energy that, after it penetrates those vitals, it then continues on to plow through a school bus full of nuns and orphans being followed by a limousine full of attorneys.

Ideally, the bullet should be able to offer this sort of performance even after passing through a variety of barriers, whether heavy clothing or drywall or auto glass. This is where controlled expansion comes in.

In the early days of jacketed hollow-point pistol bullets, the emphasis was on “WOW, EXPANSION!” and light bullets with heavily skived (pre-cut) jackets were driven as fast as possible in order to deliver it. The problem is that those light, fast, rapidly expanding bullets bled off so much of their energy in opening up on initially hitting the target that they sometimes failed to penetrate far enough to reach the vitals, most famously in the FBI’s Miami gunfight, where a 115-grain Silvertip stopped just short of the killer’s heart after first traversing his bicep and lung.

That shot could have been a fight-ending hit if the bullet hadn’t expanded at all, rather than expanding too much, too soon. There’s a certain amount of irony in the idea that the zoomiest, most cutting-edge jacketed hollow-point of its day, performing exactly as it was designed to perform, failed crucially in a shot that would have been perfect if it had been made with a 10-cent round of cheap-o military surplus FMJ.

As a result of that incident, the modern ballistic-testing protocols arose at the FBI and, having an objective and demanding standard to meet, ammunition companies designed reliably expanding, deep-penetrating pistol bullets to meet those standards.

These days, all the major manufacturers offer loads that have been rigorously tested and street-proven, and it’s only a matter of finding one that functions reliably and shoots accurately in your carry piece.

Discover how you can join nearly 300,000 responsibly armed Americans who already rely on the USCCA to protect their families, futures and freedoms: USCCA.com/gunsamerica.

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{ 3 comments… add one }
  • Larry C. June 21, 2019, 8:43 am

    It would be a series of limos.

  • Adam June 18, 2019, 12:19 pm

    We’ll have to agree to disagree on the limousine full of attorneys 😉

    • perlcat June 21, 2019, 10:32 am

      I believe author is referring to the limo full of attorneys as waiting to pounce upon the shooter, not as a series of targets. Now, if said attorneys were useful enough to stand in a conga line, we could use them as a form of ablative armor to shield busloads of nuns and orphans. It there were exactly enough of them to fully deplete the bullet’s momentum, that would be optimal. We as a society do not need an excessive number of them beyond that number; we have no use for leftover attorney-based ablative armor. Optimally, they would be jacketed by a layer of gun-grabbing demogogues, but they usually stand on *top* of dead children to make their bid for election, and as a consequence, it is hard to get them to stay at the front of said conga line. One can only dream.

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