Killin’ Science And Bullet Selection For The Layman
By "TresMon" ( 'net name) Tres Monceret
A fun but educational look at terminal ballistic science.
[I received the following question in e-mail and it turn it sparked an article. Around here "articles happen. "]
"Out of curiosity, how can a game warden tell if a deer was shot with a
muzzleloader or a rifle?"
Well, besides the obvious that anybody would know - the entry wound size and shape - it's forensics. A low velocity big bullet is more of a mauler internally; it's just brute force mashing its way through the meat. A high velocity rifle bullet kills more actually by hydraulics than by hemorrhaging (blood loss/circulatory damage.) Most modern hunters know that "energy kills," that is, energy is the biggest, baddest killer. They just don't know how to explain it.
All animals are mostly water. So think of this. Imagine hanging up a waterproof full sized punching bag that’s full of three day old mash taters. You know the ones that have increased their viscosity some. Now shoot a scalpel through it. What did we observe? The bag did not move or swing much. It was not a dramatic looking event. We have a hole through both sides of our bag that is leaking pretty fast. And if we were to dissect the bag and mash taters we would see merely slits through the wound "channel". But the "hole" or wound channel is tight, meaning from the elasticity of the mash taters "meat," the channel drew back up on itself, not 100%, but mostly.
There's your broadhead, spear and Atlatl killed deer. (Yes, spearing is STILL legal and actually STILL done in a few states. A few of my hardcore wilderness survival friends do it.) This is death by hemorrhage alone, or bleeding out, internally and a little externally. Sure, the deer experienced some energy, but no more than a major league batter getting beamed in the shoulder by a fast pitch. Not enough to kill or long term injure.
So now let's move to big bore pistols and muzzle loaders. So we shoot our hanging tater bag with a .357 mag, .41 magnum, .44 magnum, etc., or a front stuffer. Now we have energy doing some amount more of the killing than hemorrhage. And we have not just a wound channel now but also a wound cavity. What did we observe? The front of the bag was displaced or caved in a good bit from the energy. The whole bag is swinging some back and forth. We have a small hole all the way through our bag that did not seal back up. This is our wound channel. But the front side of the hole or entry side is where our channel is larger than bullet diameter and it slowly tapers down as we move deeper through the channel. This is the PERMANENT wound cavity. To explain temporary and permanent wound channel, I need to explain the hydraulic effect of a bullet.
The hydraulic effect of a bullet hitting the watery meat and core of an animal: Newton's law says, "Reckon for every tough lick thar's a equal and opposite nuther tough lick." So we observed in our front stuffer shot on the bag, the surface of the bag was displaced. That’s energy from the bullet being dispersed into our target. So let’s say we were shooting a .451" 45 cal. slug. If we shot a basically 1/2" piece of metal at the tater sack, how come the displacement on the surface was so much larger in diameter than the slug? Energy! Energy does amazing things.
Enter the temporary wound cavity. When a moderate to very high energy round enters our taters (meat/flesh), the energy damages and destroys tissue far larger than the bullet diameter. Initially energy from the bullet "blows" a quite large cavity or space in the tissue. But it does not stay this size of a space. The immediate size of the empty space or cavity is called the temporary cavity. From the amazing engineering God designed into flesh, due to the elasticity of the flesh, it will attempt to shrink back down and come back together. So this big hole or cavity we blew into the near side of our tater sack will immediately begin to shrink. And again we learned this is a temporary cavity. But we transferred such a large amount of energy into the flesh that we destroyed much of it. Due to this, though, it will shrink back down a good bit. It will not shrink all the way back down to the actual bullet diameter hole the bullet drilled into the meat. This is called the PERMANENT wound cavity. Here's a pretty good example of a temporary, permanent wound cavity and wound channel: [I'm referring to wound "channel" as the small bullet diameter hole that goes beyond the cavities.]
So why does the permanent cavity exist far larger than the actual diameter of the bullet that created it? Why does the temporary cavity not shrink all the way to the physical bullet diameter that passed through? Well we already said because the immediate tissue was destroyed but let’s take a closer look. We'll recap for a second.
We shot a scalpel through our 100 lb. mashed tater filled punching bag. We ended up with a snug little leaking hole. This will kill the tater bag, but slower, and it certainly will not be dramatic.
We shot our bag with a front stuffer. Cool. For a split second we caved in the front of the bag. The whole bag is swinging. More cool. Now we got a little bitty "junior sized" football shaped hole in the near side of the bag of taters and a 1/2" hole all the way through. Way cool.
Now let's shoot our tater bag deer simulator with an American favorite: the .270 Winchester. If we could see the hit in slow motion we would see the waves of energy rippling the surface of the bag. It literally looks like the concentric rings coming from a stone dropped in still water. We significantly displaced the surface of our tater sack. It's swinging pretty good overall. We go to examine it and see we have a full sized football shaped "wound cavity" in the near side of tater sack and a bullet diameter hole the rest of the way through.
[Cavity dimensions and "football size" references are not literal, nor dimensionally accurate, nor have I ever shot “mashed taters.” They are merely used to illustrate to the reader’s mind familiar mediums and sizing/shapes, while conveying what’s happening on/in target accurately overall.
It's hard to draw a series of pictures in a reader’s mind, but in doing so with these familiar shapes and references, I feel I have transferred the actual science to the reader accurately.]
So what is happening in that instant the bullet transfers energy into the medium? That's the hydraulics we were talking about, essentially a violent water column radiating out from the bullet entry point. From scalpel to bullet "energy wand."
So the scalpel made no real cavities at all. Our high velocity rifle round made a serious temporary and permanent wound cavity. So let me illustrate what this hydraulic water column does. Back to our hanging 100 lb. mashed tater filled punching bag. This time we hang our tater sack in the bay of the high pressure car wash. We again are armed with our .270 Win but let's dump out our taters and fill our bag with well cooked green peas. These green peas represent cells, the individual cells tissue is made of. When we introduce energy into tissue from a blow, the water contained goes the equal and opposite direction, violently! Think of if we dropped $1.50 into the slot to activate the high pressure sprayer of the car wash. We stick the wand down into the peas and pull the trigger. What happens? The water pressure basically makes the immediate peas seemingly vanish, the closest mangle, and the furthest affected by the water to burst and leak.
That’s a good verbal picture of what is happening to tissue when massive amounts of energy are transferred from a bullet to flesh due to hydraulic energy forces, and it's quite understandable that as amazing as bodies are, some tissue, i.e. the permanent wound cavity, does not recover.
So this is the way we actually kill targets. So what do we do with this information? We wish we our military could shoot terrorists with expanding hunting type bullets! We can use our new found knowledge of energy transfer from bullets to mash taters to better select the weight and style of bullet we shoot. Bullet selection all depends the on the average size, weight and range of the mash tater sack we are hunting. You see, there are three schools of thought with hunters. The first is the antiquated and Neanderthal thought: "make the biggest hole" [wound CHANNEL] you can - all the way through the animal, to produce maximum amount of (blood) leakage."
And the second sounds so clean, sterile and harmless on the printed page: Transfer all the energy. Sounds ho-hum, boring. (But it’s incredibly devastating and violent!!!)
The third school got high in the bathroom and don’t care. They just like to hunt.
Think of this: A bullet moves because energy has been imparted to and into it. Once it leaves the bore, pressure is relieved from the firing system and the bullet got what it gets and is now leaking energy slowly into the really low viscosity water we shoot through called air. If you ever have a conversation with a bullet it will refer to same as drag. If it runs out of energy it would stop forward motion in place, spent. (If there were no gravity.) There! You get it! Wait, you look uncertain. I'll give it to you: You want the bullet to stop. IN the target. Why? Transfer. Energy transfer. 100% wicked violent energy transfer. You see, if your bullet, regardless of caliber, diameter, weight or speed passes through the target and travels beyond, it did not give you its all. Any energy the bullet had to travel beyond our tater sack was wasted. We could have dumped that leftover energy into the mashed taters as well for an even bigger car wash wand effect!!
So there it is. With a high velocity, high energy round we want a complete energy dump into our wild free range 12 tined tater sack we so carefully stalked. That’s why there are so many bullets to choose from for a given caliber. Enter bullet (a.) design and (b.) weight. Real world example: I know a well meaning greenhorn who was new to shooting, new to rifles and new to hunting. He went on a coyote sized furry predatorial tater sack hunt with a friend and was hooked. So he decides he needs a good rifle, camo and a few calls. Talking about his new love on the job a coworker offered to sell him a like new ultra lightweight 300 Win Mag complete with scope, for an incredibly low price. "Because it will kick your teeth out," the guy said. So our young greenhorn figured one, that "he could take it," and two, that all that power would for sure blast a dog sized fur covered flea infested mange pocked mashed tater sack into the next siriometer or so. He took the rifle.
So Mr. G. Horn went and bought some 300 WM ammo, on sale. Winchester 180 grain Power Point factory loads. A real world MOOSE load. (He did not do the math I'm sure. I'll do it for him: 3500 ft. lbs. of car wash wand effect at the muzzle.) Looking at the big shiny menacing ammo, I'm sure Mr. Horn was sure it would blast the doggish creature for at least a siriometer!!
So after a while he calls me. "Man this thing really, REALLY kicks!" I chuckled, having been there, done that in my youth. I threaded his barrel and installed a nice muzzle break. He was really happy with the recoil reduction and off he went. Soon enough he made his first "I got one!" phone call to a buddy. But he was quick to tell me the critter just limped about 20 paces and died. No siriometer. I chuckled, having been there and done that in my youth, and explained bullet selection.
You see, if Mr. Horn had hand loaded him some little bitty 110 grain Sierra hollow points at an anemic (for the Win Mag with this bullet) 3200 fps, he would have opened up that critter like a book, displaying its most every deep and inner thing, literally. True, the little bullet would had a good bit less energy, 3200 lbs., But it would given Mr. G. Horn its all!
The little bullet would have disintegrated in the critter for a 100% energy dump, whereas the moose bullet that was actually used likely zipped right through with no "upset," commonly called expansion or mushrooming, on behalf of the bullet in the 35 lb. target. After all, that load was designed to hold together, burrow deep and energy dump in a dangerous big boned hardy built massive tater sac weighing upwards of 1700 pounds for the Alaskan-Yukon variety.
Speaking of bullet upset, there is fascinating engineering that goes into bullet design. You see that dumb piece of metal we call a "bullet" has no intelligence nor on board computer, but must juggle the depth of penetration/energy dump act to perform its best. And to compound this complexity, it must do it anywhere in an extreme velocity spread. If we shoot our massive moose tater sack and the bullet disintegrates on the shoulder muscle, we have wounded him, he’ll run off and we may have lost him and wasted the meat. If the bullet zips through him without hitting a vital organ, we again have wounded him and likely lost and wasted him. Enter bullet engineering.
A bullet upsets and begins to expand. This ever increasing blunt frontal diameter increase increases the difficulty for the bullet to penetrate. This rate of expansion must be carefully controlled through inherent design to allow the bullet to expand slowly enough so it can burrow 1: Deep enough to get past the near side muscle and into the vital organs, but 2: Fast enough to not completely pass through the animal, thereby wasting energy.
That would be a feat of engineering if the bullet hit the mash tater sack at the same speed every time. But it’s always impacting at differing speeds. If we engage our 1700 pound marsh wading mashed tater sack at 220 yards, the bullet will impact at far greater velocity than it will if fired from a long range hunter engaging our swamp tater at 1106 yards. Either way, the bullet must not under or over expand to penetrate sufficiently and energy dump. And amazingly, they get it right most of the time!
In conclusion, bigger is not always better in regards to quick, clean ethical kills, whether the subject of discussion be "which cartridge?" or "which bullet?"
"A man with an experience has volumes more than a man with a theory."
Tres MonCeret is a career machinist, gunsmith, competitive shooter, writer and instructor of many modern and primitive outdoor topics. He is currently looking for work in one of these venues in any geographical "cool place" to live. Resumes available.