Author Topic: Terminal Ballistics of pellets  (Read 313 times)

Alan

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Terminal Ballistics of pellets
« on: July 19, 2018, 08:28:35 AM »
Internal ballistics (what happens inside a weapon propelling a projectile), and external ballistics (the flight of the projectile after it leaves the weapon) are well known sciences. In fact, knowing just a few basics like velocity, the BC (Ballistic Coefficient), and the SD (Sectional Density) of the projectile, along with the ambient conditions, and one can closely predict the flight of any projectile.

Once the projectile in question reaches its intended target (assuming game), the number of variables increases to the point, that science has very little to do with the actual damage inflicted, lethal or otherwise. But that doesn’t stop folks from generating all manner of anecdotal evidence. One very good example is the use of the term, Hydrostatic Shock! Another is Stopping Power! Both of these terms, don’t mean much, especially in the world of pellets!

By pellets, I’m speaking of sub-sonic, diabolo-shaped (wasp waisted) projectiles, not bullets! If we were talking about the latter, here is the definitive, on-line treatise: http://www.rathcoombe.net/sci-tech/ballistics/wounding.html If you take time to wade through the material, you’d notice a lot of applicable material. However, the author is speaking of (for the most part) super-sonic projectiles. With few exceptions, pellets are shot at sub-sonic velocities. Therefore, my consummate opinion is, that pellets are in a class of their own, and that super-sonic data, gathered by whatever means, is not applicable!

While I was formulating my thoughts on this subject, I even thought about including a comparison between pellets and mini-balls, like those used during the American Civil War. But as I thought about it, mini-balls were really large (≥ .45 caliber), the use of soft lead alloys notwithstanding. In any case, the analogy isn’t applicable. Nonetheless, I believe pellet shape is very important!

At this point, there could be an in-depth discussion of the various types of pellets, but most have a finite use. Wadcutters are a good example, while they might make good hunting pellets at close range, their flight characteristics are not conducive to hunting game at longer distances. The same could be said for hollow points. Some may argue, but I consider PolyMags to be short range designs as well. This leaves us with the pointed and round nose pellets.

I’ve not had good luck with pointed pellets either, especially so in either of my .25 caliber airguns due to nutation. The primary cause for the nutation remains unclear. One of the brands I tried had longitudinal striations on the skirt. As a result, defection due to Magnus effect was more pronounced! Further, their kill ratio (by personal observation) is less than half of that of the round nosed pellets I’ve settled on. Perhaps it is because they tend to push aside tissue, rather than bore thought. I’ll leave that issue up to the readers.

One thing is for certain; The vast majority of airgun pellets are round nosed. And, I believe some of the reasons are not well known. For example, about four years ago, Bob Sterne posted a drawing on GTA (https://www.gatewaytoairguns.org/GTA/index.php?topic=68209.20) as shown below. Yes, there are variations in the actual ogive between manufacturers, but those differences are rather slight. Remembering that pellets are both spin and drag stabilized, it stands to reason that round nosed pellets provide better overall flight characteristics (at extended distances) than other designs. It has certainly been my experience that they do! Nonetheless, here’s something else to ponder.

What if it turns out, that round nosed pellets provide superior terminal ballistics than any other design? As I alluded to above, I believe they do! One might argue that some pellets are softer than others, and this (that) variation in hardness is the reason for the superior terminal ballistics. But I believe the hardness is a secondary issue, not the primary one. If you have differing opinions, I’d like to hear them.




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Alan

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Re: Terminal Ballistics of pellets
« Reply #1 on: July 19, 2018, 03:44:55 PM »
Terminal ballistics aka "How I shot my chrony"   ;D ;D ;D

So what do you hope to learn from your study of terminal ballistics? 

Ballistics that provide the most accuracy?
Ballistics that provide the most range?
Ballistics that carry energy the most efficiently? (discounting solids, as discussed).

I'm kind of interested in when we change our description from diabolo to solid "bullet"?  For example, the JSB Monsters and H&N rabbit magnums really cross the line. 

Also, a comparison with heavy diabolos (Eun Jin?) and a solid of the same weight would be interesting.
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Alan

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Re: Terminal Ballistics of pellets
« Reply #2 on: July 19, 2018, 06:11:50 PM »
If I didn't make it clear...

I just so happens, I believe, that the optimal shape of a pellet for long distance accuracy, also happens to be the best shape to deliver the best terminal ballistic performance. And, as I alluded to, the softness of the lead is part of the formula, but of less significance.

How's that?
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Alan

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nervoustrigger

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Re: Terminal Ballistics of pellets
« Reply #3 on: July 19, 2018, 07:10:11 PM »
Well, terminal ballistics has a rather narrow definition:

Quote
Terminal ballistics is the study of how a projectile behaves when it hits its target and transfers its kinetic energy to the target.

By this measure, a wadcutter wins the prize.  Certainly transfers more of its energy and produces more tissue damage.  The one caveat is that it must be moving with enough velocity to ensure some significant penetration.  In other words, if we were to stack the deck so a dome was moving just fast enough to barely penetrate, the wadcutter would fail to do so.

But of course that advantage quickly erodes as distance increases, and domes are quite capable of getting the job done when they icepick gray matter so wadcutters tend to have a practical range limit of 30 yards or so for the types of small pests we typically deal with...house sparrows, chipmunks, gray squirrels, etc.
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Alan

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Re: Terminal Ballistics of pellets
« Reply #4 on: July 20, 2018, 04:01:56 AM »
And that is one of the points I tries to emphasize—distance.

I can't speak for anyone but myself. My average shot distance is over 40 yards, and it is not uncommon to have 100 yard shots.
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Alan

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Bullfrog

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Re: Terminal Ballistics of pellets
« Reply #5 on: July 21, 2018, 09:22:09 PM »
I agree that round nose probably has the superior terminal ballistics, but for different reasons. My take, after killing a lot of larger game, is that the primary damage comes from the pellet's skirt cutting the flesh in a 360 cut as the pellet flies and spins thru. If I'm correct, that would explain while non-deforming 31 gn, .25 Barracudas and 81 gn .357 JSBs can be so deadly on lung shots. Neither pellet deforms in any significant way and offers superior penetration to softer pellets that deform as they pass. After shooting rigid pellets like that into ballistics gel, the boat-prop wound channel I get seems consistent with the skirt cutting as it goes.

So under my theory, the superior pellet in many circumstances will be the one with a rigid, non deforming body that will maximize both penetration and retained shape of the skirt and forward directional travel of the pellet.

I don't discount that expanding or deforming pellets can be deadly. But I think the expanding of a pellet's head is is a different phenomenon all together than the cutting caused by the skirt. An expanding pellet (or a bullet for that matter) is cutting and/or ripping as it goes, but its a very different kind of wound than what a pellet's skirt is making.

In small game, I generally want an expanding pellet. In large game, I want deep penetration and a cavity that looks like a cookie cutter has been ran thru the lungs.
« Last Edit: July 21, 2018, 09:28:52 PM by Bullfrog »

Alan

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Re: Terminal Ballistics of pellets
« Reply #6 on: July 22, 2018, 04:09:32 AM »
I would tend to agree with your assumption. Especially so when we take into account that pellets are both spin and drag stabilized. Body flesh and fluids are certainly thicker than air, which could cause a wobble (nutation) once the pellet hits its target, thus allowing the skirt to do even more damage. A high speed camera would certainly prove the scenario.
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Alan

I have an Omega compressor. If you're a fellow Guild member, and you pass through Roswell, NM, I'll fill your portable tank as a courtesy.