Author Topic: What DOES penetration + damage really depend on? – Hunter’s Terminal Ballistics (Read 1821 times))

JungleShooter · « **on:** September 13, 2018, 07:54:31 PM »

When we plink to destroy, and when we hunt to kill – what does penetration and damage really depend on?

• Say both Pellet A and Pellet B arrive at the target with 15FPE.
• Pellet A weighs 25gr and arrives with 520fps at the target.
• Pellet B weighs 15gr and arrives with 671fps at the target.
• Let’s assume that the shape and hardness of both pellets is the same (of course, due to weight difference they aren’t).

Q1: Which will penetrate more in flesh?

Q2: Which will produce more damage (permanent wound channel)?

There are these concepts of momentum..., kinetic energy..., and foot-pounds of energy (FPE)....
I had thought that for the same shape and hardness of a hypothetical projectile, the FPE at the target is all that counts.
However, I read conflicting comments sometimes. Somehow, some say the weight is also important. Others yet, the velocity at the target is important.

I guess I need some help tying these concepts together.

Thanks!

bandg · « **Reply #1 on:** September 13, 2018, 08:15:04 PM »

That's opening a can of worms right there!

JungleShooter · « **Reply #2 on:** September 13, 2018, 08:25:25 PM »

Rather than worms on the fishing supply store shelf, I was more thinking of pigeons and rabbits in the wild....

But, I get it, bandg, this is complicated.
That's why I asked, since I've read quite a bit on this and I'm still confused....

Horatio · « **Reply #3 on:** September 13, 2018, 10:30:22 PM »

The diameter of wound channel should be similar I think if both are domes.

The one with greater sectional density should penetrate deeper, if both are shaped the same.

If you are looking for greater wound diameter, go with the faster one in an expanding head design.

I don’t think any of it matters much, as long as you put the pellet where you want it.

makoda · « **Reply #4 on:** September 13, 2018, 10:48:57 PM »

I think the faster one will penetrate bone better but chest shots won’t matter much either way. Just my guess.

subscriber · « **Reply #5 on:** September 14, 2018, 12:57:14 AM »

Matthias,

In the grand scheme of things, both of your test cases are "low velocity". That said, I believe the slower heavier projectile will penetrate unclad ballistics gel better. This is mostly because drag in a viscous fluid is a function of velocity squared. Perhaps switching to velocity cubed (or more) for flat or expanding projectiles.

The video below by Matt Dubber explores penetration and "wound cavity size" in a clay block of unknown condition and origin. It seems to suggest that penetration increases slightly with velocity, until the projectile starts to deform. Then added velocity may actually decrease penetration, because all the extra energy is spent making the "wound" much wider.

The waters are somewhat muddied because while all of Matt's "pellets" are .22 caliber, they vary greatly in shape, mass, construction and type. Certainly, the 80 ft.lb 40 grain roundnose solid projectile behaved like a softnose projectile at those energy levels:
www.youtube.com/watch?v=xXhg9J44mWk

Ballistics gel may be regarded as an accepted flesh substitute for wound cavity research. However; except for a confluence of factors that happen to provide useful comparative PB bullet performance, gel is nothing like flesh: Flesh is made up of very strong fibers, that gel lacks. Living flesh is much "wetter" than ballistics gel. Gel is just wet enough to cling to and drag on the projectile, like a wet T-shirt does. The effort to cut open gel blocks to retrieve projectiles shows that it has almost no strength, and that the model relies primarily on the displacement of "fluid" mass and viscous drag. What makes clear gel good, is that it leaves a visible bullet path; and is capable of some stretch to study temporary cavitation.

Obviously, there are no bones in ballistics gel. That is why some people who are keen to tease out more realistic penetration and expansion results will often place a rack of lamb on either side of a gel block that has the depth of the target animal torso. Even covering it in clothing, if the projectile under evaluation is intended to stop people.

Penetration of bone is perhaps closer to penetration of sheet metal, in that a "threshold velocity" is required. That is where the analogy ends; as bone is brittle, while mild steel for example is very ductile. Perhaps a spaced stack of two thin ceramic tiles on either side of the "torso" or "skull" may offer a better model for bone. Such tiles don't seem to be used nearly as often as cinder blocks to study bullet penetration. And then the latter represent walls, rather than bone.

Threshold velocity for penetration is somewhat of a variable, being lower for heavier and sharper projectiles (high sectional density and pointy; like an arrow). At sufficiently high velocities, bullets punch clean holes through sheet metal, very "efficiently": This is seen as very little displaced metal around the edge of the hole; with the bullet retaining a very high percentage of its energy after penetration.

At lower velocities, the dent around the hole is much wider radially, and much deeper. Retained energy of the bullet much lower, as more was spent creating the larger area and volume of damage. The mechanism that favors high velocity here is inertia of the target. Inertia is a function of the abruptness of the event; where higher velocities produce more abrupt impact. Skin also has a threshold velocity for penetration, that behaves somewhat similar to sheet metal; except that skin is much more flexible.

Getting back to Matt Dubber's clay block test; if he had been shooting the equivalent of full metal jacketed handgun bullets, I predict the penetration would have been much deeper for the 80 ft.lb Huben. A hard heavy non expanding round nose projectile at moderate velocity penetrates animals very deeply. That is why big game hunters use large caliber heavy solid bullets at low velocities (for a rifle) on dangerous game. These don't need to expand to create "wide enough" wounds; that can often penetrate the full length of a cape buffalo; or penetrate through to the brain of a charging elephant from any angle, other than from behind.

So, your penetration question needs to be refined by including the type, size and placement on the target: Are you talking about penetration of a wild pig's skull on the sloping frontal section, or through the body of a rat?

Either way, at 520 to 671 FPS you are talking about a pellet diameter hole, equal in length to whatever it managed to pass through. For small soft animals, that is the extent of the damage. If that path does not include major organs, you are just wounding the animal. If it includes the brain, heart, or lungs, a small animal will drop on the spot; or expire in less that a minute: Consider that a sparrow taking a .22 pellet is like a human taking a 4" diameter cannon ball. No expansion is required, and full penetration is guaranteed; even at only 500 FPS. Percentage wise; that is a lot of crushed tissue...

subscriber · « **Reply #6 on:** September 14, 2018, 01:15:59 AM »

Also see this thread on the same topic: https://www.gatewaytoairguns.org/GTA/index.php?topic=147820.0

rsterne · « **Reply #7 on:** September 14, 2018, 01:32:22 AM »

Matthias, you don't specify a caliber, but judging on the weights I will guess .22 cal.... Penetration of non-expanding projectiles of similar shape, in a constant medium, is proportional to the product of the Sectional Density and the Velocity.... If the caliber is constant, then it is proportional to the Momentum, not the Energy.... Although they both arrive at the target at 15 FPE, the heavier pellet will have more Momentum....

Momentum = Mass (lbs.) x Velocity (fps)
For the 25 gr. it is 25/7000 x 520 = 1.86 ft.lb/sec
For the 15 gr. it is 15/7000 x 671 = 1.44 ft.lb/sec
Therefore, the 25 gr. pellet should have about 29% greater penetration

If the pellet does not expand (if it does, the SD changes, and the above comparison is not valid), then the wound channel should be the cross sectional area of the pellet times the distance it penetrates.... That would mean the volume of the wound channel would also be 29% greater for the 25 gr. pellet, compared to the 15 gr. pellet....

Of course if either or both pellets penetrate completely through the animal, then the length of the wound channel will be the length of the passthrough.... so they could very well both have exactly the same terminal ballistics on a small animal.... What subscriber say is 100% correct, unless you hit a major organ, you have a wounded animal either way....

Bob

JungleShooter · « **Reply #8 on:** September 14, 2018, 05:18:05 AM »

subscriber, your wound ballistics are very helpful. Your idea of a threshold velocity is excellent for bone penetration. Your link to Matt Duber’s video makes me want to have a more powerful gun... Thanks for your very clear explanations!

Bob, yeah, I had hoped you’d chime in. Thank you. That formula stuff, that’s what is hard for me, but I want to understand.

So, I get this so far:
• Same caliber: Penetration =>proportional=> Momentum
   Momentum = Mass (lbs.) x Velocity (fps)

Is the following then true (or what is the right formula?)?:
• Different caliber: Penetration =>proportional=> Sectional Density x Velocity
   Sectional Density = Caliber (in.)^2 x Mass (gr.) / 7000 [correct?]

• For an expanding pellet, i.e., a pellet with “changing caliber”, the same formula applies?
   Penetration =>proportional=> Sectional Density of the expanded pellet x Velocity

Yet I’m still wondering how momentum and energy (ft.lb) relate to each other. And why "everyone" seems to be talking much more about energy retention at the target, than momentum.... In the same vain, why does ChairGun Mobile only give me the ft.lbs at the target, if the more important figure is momentum?

bandg · « **Reply #9 on:** September 14, 2018, 11:17:27 AM »

I would listen to Matt Dauber on this issue. The guy probably has more actual hunting experience than most and has studied both air guns and PB's extensively. He's pretty good at making graphs and data understandable as well.

Mole2017 · « **Reply #10 on:** September 14, 2018, 11:23:21 AM »

Quote from: JungleShooter on September 14, 2018, 05:18:05 AM

Yet I’m still wondering how momentum and energy (ft.lb) relate to each other. And why "everyone" seems to be talking much more about energy retention at the target, than momentum.... In the same vain, why does ChairGun Mobile only give me the ft.lbs at the target, if the more important figure is momentum?

Hmm. This discussion will be interesting to follow. I chip in:

It seems energy is a preferred measure, as that represents the available potential for damage. Consider a non-penetrating blow to the head: any discussion I've seen shows the energy required.

If the pellets aren't expanding, then your other choices are soft or hard pellet and what shape. Soft pellets at least can deform some, so maybe some marginal improvement. As for shape, pointed pellets seems to drill through things with small wound channels, like the tissue is pushed aside. Domes are a little better--slightly more damage along the path. But me and a bunch of others really like what wadcutters do--the wound channel is really at least a full diameter cut through the tissue. They make a fine mess. I've seen them just nick a blood vessel with fatal results, whereas the dome would be more likely to push the vessel aside in the event of only glancing contact.

On squirrels, pass throughs with wadcutters were rare, but they almost always stopped the squirrel. Though a pass through would happen sometimes, usually they just stop under the skin on the other side--essentially an ideal pass through then, with no wasted energy? Except maybe bleeding from two hole is better than one sometimes. I even think there is more a knock-out (or knock down) effect with wadcutters. The pellet dumps energy so quickly that the shock can stun them. With domes...well, it seems you need a little more precision to get a kill shot that is as effective. I've seen squirrels initially brush off a pass through, though it may nonetheless be fatal.

bandg · « **Reply #11 on:** September 14, 2018, 12:43:11 PM »

One might read a bit on the topic of hydrostatic shock. Obviously not something really relevant to air guns but might give a person a wider field of view considering some of the odd reactions to less than ideal shot placement often reported with ultra high velocity bullets. Could this be a factor with air gun velocities? Probably not but who knows. One thing certain-the relative size of air gun pellet to small game in relation to firearm bullets to larger game is much higher. How does velocity relate? Above my pay grade but again I'll listen to Dauber's experience.

rsterne · « **Reply #12 on:** September 14, 2018, 01:15:30 PM »

Matthias.... You've got it right.... except that often projectiles that expand also come apart, and individual pieces often penetrate very deeply.... In addition, the wound volume cannot be calculated in that case, because each fragment causes it's own channel.... check out these .257 cal HPs at 130 FPE....

Energy is Mass/2 x Velocity squared....
Momentum is Mass x Velocity....

The energy component is therefore much more reliant on the velocity.... BTW, you can add columns to ChairGun for Momentum, and even Penetration....

David, don't forget that two pellets can have the same momentum but vastly different wound channel shapes, if they are of different calibers.... Take two 25 gr. pellets, one in .22 cal and one in .25 cal.... The SD of the pellets is....

.22 cal SD = 0.07379
.25 cal SD = 0.05714

If the velocity of the .25 cal is 520 fps as per the original post, the Penetration is (some constant, depending on the medium) times SD x 520....

.22 cal penetration >(prop. to)> 0.07379 x 520 = 38.37
.25 cal penetration >(prop. to)> 0.05714 x 520 = 29.71

However, the area of the cross section of the pellet (wound channel) is....

.22 cal area = (.22 x .22 x PI/4) = 0.03799 sq.in.
.25 cal area = (.25 x .25 x PI/4) = 0.04906 sq.in.

Therefore the volume of the wound channel is area x depth (remember the depth depends on the media, this is a ratio)….

.22 cal volume = 0.03799 x 38.37 = 1.458
.25 cal volume = 0.04906 x 29.71 = 1.458

Note that the wound channel volume is the same, for two pellets having the same momentum (and energy), but of different shapes, the .22 cal punching a longer, thinner hole than the .25 cal.... Assuming the pellet does not pass through, both pellets transfer all of their momentum to the target.... However, the larger pellet, stops in a shorter distance because the tissue it passes through provides a greater retarding force because of the larger diameter (and area)…. This force can be seen in how that larger pellet has more "knock down" power.... If both pellets pass through, the observed difference is even greater, because more of the smaller pellets momentum is wasted (it could have penetrated even more)…. In addition, if the pellet expands, the SD decreases, so the penetration decreases, again because the retarding force provided by the tissue is greater again.... resulting in even more observed knock down power....

I have in the past used the expression "tissue BC" to describe how pellets slow down in flesh, just like they slow down in air.... It is not hard to imagine that round-nosed and pointed pellets penetrate further than a wadcutter, just like they lose less velocity in air.... Hollowpoints, once expanded, are even easier to understand, after all, in their expanded condition they would have a terrible BC....

…. The measurements of penetration I have made in soap clearly show that round-nosed pellets, just like they have a better BC in air than a pointed pellet.... also have greater penetration.... This might not apply to their ability to shatter bone, but in flesh it appears that the shape of a shape of a round nose pellet is superior to a pointed for penetration.... In a very hard to penetrate medium like paraffin wax or wood, this may not be the case, but is is in soap, putty or ballistics gel (for pellets of equal caliber, weight and velocity)…. Flat-nosed pellets, because they slow down faster, transfer their energy to the target in less distance, with less penetration, and that is observed by them "hitting harder".... and HPs even more so....

Bob

guero_gordo · « **Reply #13 on:** September 14, 2018, 02:11:12 PM »

Quote from: rsterne on September 14, 2018, 01:15:30 PM

Energy is Mass x Velocity squared....

It's one-half MV^2

rsterne · « **Reply #14 on:** September 14, 2018, 03:55:56 PM »

Darn I hate it when people read what I write....

Nice catch, I fixed it above....

Bob

Bryan Heimann · « **Reply #15 on:** September 14, 2018, 05:47:57 PM »

Velocity and weight work together for penetration. More velocity means more penetration as long as the round holds together, more weight also gives more penetration in a given diameter as long as it doesn't tumble.

At the end of the day, with an air rifle that has adequate power to kill the animal, the most important factor in pellet selection is accuracy.

xtred1 · « **Reply #16 on:** September 14, 2018, 08:49:29 PM »

It truly depends on the job to be done. The numbers you talk about and the game you talk about the difference is pretty insignificant.

JungleShooter · « **Reply #17 on:** September 16, 2018, 05:47:31 AM »

Thank you all for your detailed and well-written explanations. I see some differences clearer now – wider wound channel vs. longer wound channel (penetration depth).
The concept of penetration threshold velocity is really helpful as I have been asked to do some lethal pest control on larger animals. This really expanded my thinking about pellets needing to penetrate skin, fur, feathers (wings!), and/or bones (skull!) before doing their lethal damage. I found a lengthy paper that talks about this.*

Bob, your tissue BC is a beautiful concept, good idea.

On some ballistic site I read that hydrostatic shock is not much more than an unproven theory (and at our velocities out of the picture anyhow).
And I read that this energy transfer business is not really what matters – but what is done with this energy: Does it make a huge temporary wound channel, that does not really destroy (crush or cut) anything, or does it crush/ cut tissue, preferably vital organs (lungs, heart) or some part of the CNS (central nervous system, i.e., brain, spine)?

Well, I kept surfing and found this article by a Dr. Ashby, bow hunter and probably THE arrow terminal ballistics research expert in the world. His article explains why all three are important for lethality – sectional density + kinetic energy + momentum, and how they relate.
The link to his article: https://www.grizzlystik.com/Ashby-On-Momentum-Kinetic-Energy-Arrow-Penetration-W19.aspx
Or here: http://www.thudscave.com/npaa/articles/howhard.htm

Some of his research is summarized in these graphs – I think we airgunners could get some ideas of how terminal ballistics research in our field could look like.
https://www.grizzlystik.com/Ashby-Graphs-W24.aspx

More scientific articles are here: https://www.grizzlystik.com/Dr.-Ed-Ashby-Reports.aspx

Anyhow, I have to digest all this now, and come up with a plan what to shoot, and if I want to get into any kind of testing....

* https://books.google.com.pe/books?id=1jHNBQAAQBAJ&pg=PA196&lpg=PA196&dq=%22penetration+threshold+velocity+%22&source=bl&ots=VtPvTjC2kw&sig=d7p2QC70m7FUt60PJ6mrGMuExDQ&hl=en&sa=X&redir_esc=y#v=onepage&q=%22penetration%20threshold%20velocity%20%22&f=false

Back_Roads · « **Reply #18 on:** September 16, 2018, 10:26:55 AM »

Glad I got side tracked when Subscriber mentioned a wet T-shirt

anti-squirrel · « **Reply #19 on:** September 16, 2018, 12:06:58 PM »

Wound channels and penetration are both effectively a wasted argument on pigeons. A hit with an airgun at 15 FPE will kill it. Why? I have thousands of fatal shots on pigeons- the only time they did not die instantly was on the very rare occasions back then I hit a leg. A head or chest shot at 15 pounds kills it dead.

Squirrels? Subject for intense debate, but I used to only take headshots and nothing else. I've expanded my bag of tricks to heart/lung shots. I know my sub-10-FPE CZ 634 has a number of squirrel relieved from life using wadcutters.- but in every instance these were headshots. I also went about the gory and messy task of grabbing those squirrel bodies, hanging them up, and taking shots to determine the best choices for my current airguns. IE: what was needed to execute a "perfect kill shot" which meant stripping the fur off the head and shooting the skull to determine lethal force required. What proved most interesting is- at my shorter ranges, the wadcutter and Polymags reign supreme, with a special mention to the Coal Fenix dome since it has a lip around the base of the dome. These things shatter squirrel skulls our of my SPA PCP pistol.

I guess in simpler terms: when looking to objectively measure and compare wounding/penetration on small targets with relatively fragile bodies (pigeons), use the most accurate pellet.

When over-penetration maims the animals (squirrels) and causes a lingering death, use the most accurate pellet.

I'm not saying this isn't worth a debate, but accuracy matters more than anything, and headshots will just about guarantee a fatality.

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What DOES penetration + damage really depend on? – Hunter’s Terminal Ballistics

Author Topic: What DOES penetration + damage really depend on? – Hunter’s Terminal Ballistics (Read 1821 times))