Home Forums Hunting & Shooting Ask The Gunwriters Mid-August column: How Hunting Bullets Expand

HOW RIFLE BULLETS EXPAND

Many hunters believe expanding hunting bullets vary considerably in how quickly they “mushroom,” due to how the bullet’s constructed. In reality, most start to open immediately upon hitting an animal, and how long it takes for the bullet to fully expand also doesn’t vary much (though there’s an exception we’ll examine later).

Unless they don’t open up at all, most expanding bullets fully mushroom within one to 1.5 times their own length. Most “deer” bullets are around an inch long, so are fully expanded by the time they penetrate an inch or so, but even the heaviest expanding bullets are only rarely as long as 1-1/2 inches. This means the deepest they penetrate before full expansion is around two inches. All of this has been demonstrated many times both in test media and game, even if the bullet’s “hardness” varies, but two newer kinds of media have revealed some very interesting aspects of bullet expansion.

One is clear ballistic gelatin, which when combined with modern high-speed digital photography allows us to actually watch expansion as a bullet enters a block of gelatin. Some bullet companies now include slow-motion videos on their websites.

The other was the Test Tube, made of a wax somewhat harder than ballistic gelatin. (It’s now out of production—though I still have a bunch.) The wax retained the shape of the wound channel, and when sectioned provided an interesting comparison without high-speed digital video equipment. Here’s a photo of two Test Tubes, the top tube shot with a Nosler Partition and the bottom tube with a Barnes TSX:


Note that the initial, wide portion of the Partition’s wound channel is thicker and shorter than with the Barnes TSX. This occurs because the Nosler initially expands wider, due to its front lead core, then loses some of the core. The Barnes doesn’t expand as widely, the reason the initial wound channel isn’t as wide, but in test media the Barnes typically doesn’t lose any weight. As a result the wound channel remains about the same size as the bullet continues to penetrate, narrowing after the bullet starts to slow down considerably.

With both bullets, however, the initial wound channel starts to widen as soon as each bullet enters the Test Tube. This also occurs in high-speed videos—and animals. On an African safari I shot a male impala with a 286-grain Nosler Partition from my 9.3x62. The ram stood angling almost directly away at a little over 100 yards, and the bullet angled steeply into the ribs, exiting the front of the chest. The beginning of the bullet’s expansion can be plainly seen not just on the ribs but the skin:


The lighter “tail” to the left of the entrance hole was made as the side of the bullet skidded along the hide. When it dug in a little deeper, the soft lead point encountered the hide, and the bullet immediately started to expand. Note the similarity of the wound along the ribs to the channel from the Partition shot into the Test Tube. This initial expansion is exactly why the greatest damage done by most expanding bullets is not far beyond the entrance hole, whether to meat or internal organs.

It’s also why big game bullets expand even on pretty small animals. I once took a reproduction Winchester High Wall in .30-40 Krag on a prairie dog shoot, loaded with 180-grain Nosler Ballistic Tips at 2400 fps. Mostly I wanted to practice with the adjustable tang sight at various ranges before hunting big game that fall, and the very first dog was a typical adult, about two inches thick through the chest. The bullet landed in the chest, where I’d aimed, and while the Ballistic Tip didn’t “explode” the dog, it flopped it right over—and there was an exit hole about an inch wide on the far side, indicating the bullet had fully expanded within two inches.

Big game bullets at higher velocity usually explode prairie dogs, despite being designed to penetrate deeper than thin-jacketed varmint bullets. This isn’t because the big game bullet expanded “too quickly,” as many shooters assume. Instead it worked exactly like most big game bullets work, expanding on impact. Yet hunters who test their big game loads on prairie dogs often assume blown-up dogs mean that particular bullet won’t penetrate on big game, when it will. (If you ever get a chance, try shooting a few Nosler Partitions at small varmints sometime. Most hunters are astounded by the results.)

Occasionally expanding bullets don’t start to open as they hit skin. Some hollow-points don’t, especially if the hollow-point is tiny, or accidentally becomes tiny by being pounded by recoil against the front end of a typical bolt-action magazine. I don’t shoot small varmints with hollow-point centerfire bullets anymore, because plastic-tipped bullets expand much more violently—and occasionally hollow-points failed to expand at all, especially at longer ranges. I’d shoot at a prairie dog and assume the shot had been a miss, because the dog would just stand there—but about the time I started to aim again, the dog would tip over, due to a tiny hole through its body.

Plastic-tipped varmint bullets expand much more reliably, including (for instance) 180-grain Ballistic Tips from a .30-40 Krag. This isn’t because the plastic tip “wedges” deeply into the core of the bullet, another common misconception. High-speed video shows the plastic tip only remains in the bullet’s nose briefly after impact, because as soon as the bullet starts to expand, the increased drag slows it down. The plastic tip then drifts ahead of the expanding bullet, and then off to the side.

Plastic-tipped bullets probably expand more violently because of the big hollow-point where the tip’s inserted, far larger than the tiny hollow-points of .17 to .22 caliber varmint bullets. Plus, the plastic-tip results in a higher ballistic coefficient, so bullets arrive with more retained velocity. A few years ago I was assigned by a magazine to field-test a bunch of different varmint bullets. To compare their performance, I used several rifles that shot bullets of about the same weight to the same point of impact at 100 yards. Plastic-tips not only drifted noticeably less in the wind at any range beyond 150-200 yards, but expanded violently at longer distances as well.

The exception to immediate expansion occurs with some of “hollow-point” target-type bullets used on big game. Most of these have VERY tiny hollow-points, often so small the point of a safety pin can’t be inserted in the hole. As a result, the bullet punches a tiny hole through the skin, and expansion’s delayed until the bullet penetrates far enough for the tip to collapse, rather than expand. You can see this bullet construction in this Berger Match VLD from over a decade ago:


This was the model of Berger that eventually was renamed the Hunting VLD, after many hunters reported they worked very well on big game, partly because of the delayed expansion. As a result, instead of major tissue damage occurring right behind the entrance hole, it started after the bullet penetrated a ways. You can see this in a Test Tube shot with a Berger:


Note how the beginning of the wound channel doesn’t start to widen immediately. Instead it remains bullet diameter, then suddenly opens WAY up at the point where the bullet expands violently. As a result, if you shoot prairie dogs with Bergers, the dogs usually don’t “explode” because the bullet does indeed pass through before starting to expand.

On big game animals, the entrance hole of Bergers is often so small you must part the hair to find the hole, and looks like somebody stabbed the animal with a knitting needle. Yet somehow many shooters insist that Bergers expand violently as soon as they impact—which only proves that they’ve never used Bergers, or any other target-type “hollow-points” that expand the same way.