Author Topic: My thoughts on terminal ballistics of pellets on small game  (Read 1094 times)


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My thoughts on terminal ballistics of pellets on small game
« on: August 26, 2018, 02:50:32 PM »
Terminal ballistics is the study of what happens when a projectile contacts its target. It can be applied to any projectile, hitting any target, for any purpose. But for this argument, it is the result of a pellet hitting small game. By small game, I mean animals of all sorts, up to the size of coyotes, just to put a limit on what we’re covering here. Yes, we’re speaking of hunting!

I hunt almost every day! In fact, the .25 caliber W.A.R. Cobra I purchased in late 2016, now has over 15,000 rounds shot through it. It has never been cleaned, yet still shoots less than 3/4 inch groups at the 100 yard, indoor range! This information isn’t to impress the reader (although it is impressive at least to me), but to add emphasis to my hunting frequency. I could expend on this, but I’ll save it for another day.

As I have stated several times before, I have always had an interest in terminal ballistics. For many years, I’ve used a litany of rifles, most of which were in 22-250 caliber. The latest one, a custom-built one, chambered for 22-250AI, with a 31 inch, 1:12 twist, Shilen barrel. The reason I chose the twist and barrel length was not the ability to shooting heavier bullets, but to increase the spin rate. With 55 grain Nosler ballistic points, the spin rated was very close to 250,000 RPM. Enough in fact, to cause some varmint bullets to disintegrate before reaching the target. But when they did reach the target, the explosive forces were a sight to behold!

But when it comes to airguns, the maximum velocity is (usually ) under the speed of sound, and typically hovers around 750 and 900 feet per second. And, the twist rates are very slow compared to your typical firearms. Twist rates don’t need to be fast, because diabolo pellets are both spin and drag stabilized.

Just for the record, I don’t want to compare airguns designed to shoot bullet-like projectiles which are only spin stabilized, and in a niche all to themselves. If there is a similarity, it is the fact they’re both made from lead alloys, and not jacked. Remember, we’re speaking only of diabolo-shaped pellets.

It should be clear at this point, that comparing the terminal ballistics of bullets with pellets is fraught with issues, most of which are easily assumed. But we mustn’t get ahead of ourselves, so I’ll state some of the obvious ones.

There is a belief in a terminal ballistic effect called Hydrostatic Shock. To say it is a controversial concept, is an understatement. And, I’ll go out on a limb with this; The concept of Hydrostatic Shock is hogwash! Just because a prairie dog explodes when hit with a varmint bullet, doesn’t mean squat! Any shock delivered to some other area of an animal, is due to bullet fragmentation, and not some mythical ideology dreamt up by some gun story writer!

What we’re really talking about, is the elasticity of living tissue, and how it reacts to being struck by a projectile. Tissue stretches to a point where it can no longer stretch. At that point, there is a momentary cavitation in the tissue close to the point of impact, followed by a wound channel as the projectile continues through its intended target. All of us have seen this effect in slowed, high-speed videos of ballistic gelatin being struck. What’s more, videos of pellets and bullets are very similar, with only the displacement area being different.

It is perhaps enlightening to watch watch the difference between a wadcutter shaped pellet, and a round nosed one (into gelatin). But in the real world, living tissue reacts exactly the same to either shape. One could argue that wadcutters impart more energy into the block of ballistic gelatin, but that’s only because of the distance to target. For example, shoot a wadcutter 75 yards down range, and there is no comparison to the damage when using a round nose pellet. The difference is due, of course, to the amount of retained, down-range energy. We’re also hoping the aforementioned wound channel passes through vital organs, causing massive bleeding and/or destruction which is the real cause of death. Let’s also keep in mind, that some vital areas are more vital that others.

There are a few extraneous arguments which I’m sure will be mentioned by others reading this treatise. Among them are Sectional Density, Ballistic Coefficient, Nose Shape and Meplat (if any), Skirt Shape and Size, and even Form Factor. However, the latter is almost as inane as Hydrostatic Shock, when applied to terminal ballistics. So let’s don’t go there. Instead, the most important factor we need to deal with, is retained, down range energy, however we get it!

There is one factor, which I am convinced plays a major role in harvesting game, at least in the world of diabolo pellets; The shape and design of a specific pellet, which inflicts the most down-range damage to animal tissue, is exactly the same shape and design which results in the best down range retained energy!

In my case, I use 25.39 grain, JSB, 25 caliber, Kings. The Cobra shoots these pellets at 880 FPS, which is very close to 45 FPE. I’ve also used Vortex 19.91 grain Supremes, PolyMag 26 grain pellets, and a smattering of others, with varying success. PolyMags for example, will not groups well past about 30 yards, and I can’t even keep them on the paper at 75 yards.

Most of my game has consisted of common pigeons (Rock Doves), Eurasian Collared Doves, jackrabbits, cottontails, squirrels, skunks, fox, and coyotes.

I don’t perform post mortem examinations on every animal I shoot, but I do look to see if the pellet exited. With very few exceptions, they do, even PolyMags. The exit wounds don’t look much different either. But based on my experience, round nosed pellets are by far the best harvesters of small game. But how can this be? I believe I know the answer.

I mentioned above about stretching animal tissue until it gives way. The resulting cavity directly behind the impact area, is the key factor here. PolyMags for example, have a pointed tip which more easily penetrates the outside layer of tissue. While they may indeed expand a bit more on their way through small game, the initial impact cavity is somewhat less than a round nosed pellet delivers.

Think about this. If you pop a balloon with a needle, it takes very little pressure to pop it. But use say a quarter inch diameter, rounded end, dowel rod, and the energy needed to pop the balloon is much more. If you try this experiment, you’ll also notice another phenomenon; The pop with a pin is not nearly as loud as the one caused by the dowel rod. The reason is, with the dowel rod you compress the air inside the balloon, resulting in a louder pop once is does. The exact same phenomenon happens with animal tissue.

Here is another point I wish to make. Most doves, even pigeons, are good to eat if prepared properly. I say properly, because most doves harbor coccidiosis, which harkens back to one of the reasons I get to hunt almost every day (which as I said, I’ll cover later). Part of the process is to wear protective gloves, and properly dispose of the discards like feathers, entrails, etc.

One thing you’ll notice during he preparation of the game, is the amount of tissue bruising at the point of projectile (pellet) entry. For example, shooting the breast of a pigeon with a PolyMag at about 25 yards, results in a bruise about 3/8 of an inch in diameter. One hit in nearly the same point with a JSB King, round nosed pellet, the bruise will be nearly 3/4 of an inch in diameter. To me, this is proof-positive of my theory postulated above.


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