Bullet performance on game (theoretical)

[stubbicatt]

Guys. I've been shooting prairie dogs with a 7.62x54r with some success. I do it because the ammo is cheaper than 223 handloads with Vmax bullets, my "other" prairie dog rifle.

But I got to thinking, as I sat there enjoying a prairie sunrise, what about deer or antelope or other "game" animals as opposed to pests?

If I understand things right, unless you are shooting a 105mm solid bullet (if such a thing exists) the wounding, or killing potential of a cartridge depends greatly on the performance of the bullet once it hits flesh and bone. As I understand it there is hydrostatic shock occasioned by higher velocities, fragmentation of the bullet due to factors which seem erratic to me, expansion of the bullet, or yaw of the bullet, which act to create a wound channel and incapacitate or kill the animal.

Each of these last three phenomenon involves creating a larger permanent wound channel than the nominal diameter of the projectile, whereas hydrostatic shock is about a temporary wound channel, which due to the elasticity of flesh, tends to return to nominal diameter, but with bruising in the tissue... not typically creating catastrophic blood loss or organ damage.

Because I really don't understand fully the erratic nature of fragmentation, my question sort of turns on either yaw or expansion. Expansion is somewhat dependent upon velocity to initiate and sustain expansion. Expansion contemplates that a bullet will continue through a game animal in a more or less nose forward attitude, but that deceleration forces acting on the material of the bullet causes a classic "mushroom" shape, with an intact shank and very little loss of mass. The result of the expansion is a larger than nominal bullet diameter permanent wound channel. Some 30 cal bullets are supposed to go to 1/2 inch or so, or 50 caliber using this method.

But what about those two or three part bullets like the 303 Brit, or the 5.45 Russian, or even the 7N1 sniper bullets fired in the 7.62x54r rifles? The designs of these bullets are not such as would cause expansion, but rather yaw and tumbling. The wounding effects of these bullets is that once they have penetrated a certain distance in flesh, they destabilize, tumbling, changing nose first attitude in attempt to obtain a heel first attitude, etc. What you end up with for at least some distance of the bullet's sideways travel is a keyhole shaped wound channel as wide at its widest aspect as the bullet is long. This can be nearly an inch in some cases.

From what I have read, the yawing effect is actually quite reliable. The bullets begin to yaw at pretty much the same depth of penetration, and the yawing is not as dependent upon velocity as is mushrooming.

Is it reasonable to conclude that the yawing bullet will create a more reliably large permanent wound channel than will the expanding bullet? If it does, wouldn't some of the 3 part "fmj" bullets be considered better hunting rounds, creating larger permanent wound channels and transferring energy to the target more efficiently?

 

[Cypress]

What happens when that non-hunting round clips bone? The problem I see with counting on the yawing effect is that it is not as consistant in an animal as it is in ballistics gel. It'll probably work just ain't good enough if you give a d@mn.

 

[Larry E]

For game animals, deer, pronghorn, elk, etc, a good expanding bullet would be my preference in just about any caliber. The military considers a severely wounded enemy to be removed from combat, their primary consideration. In hunting the efficient and humane demise of the game animal is the primary consideration. That a bullet may tumble is one thing. A modern expanding bullet will expand if it's properly selected for the game being hunted, eg, a heavily constructed bullet designed for moose or large bears may not expand on a lightly built animal like pronghorn or small deer.

Hunting prairie dogs with FMJ ammunition will certainly kill the pd's, but is also likely to produce ricochets. Not many farmers/ranchers want to have ricocheting bullets whistling past their ears, into their livestock, or buildings/equipment. Bullets like V-Max's aren't likely to ricochet - I've had them come apart on grass on the way to a partly hidden pd.

 

[sarduy]

if you hit a rabbit with a .22lr the bullet will expand due to the size of the animal and the bullet, if you shoot the same rabbit with a .50 cal even if the bullet is soft point, it will go right thrugh and you'll have an exploding ribbit because the hydrostatic shock is more than what the rabbit's body can handle compated to the hydrostatic shock of a .22

 

[MTMilitiaman]

It is basic high school physics, really.

First, Newton has a little law that states "for every action there is an equal and opposite reaction." This means that the target strikes the bullet as hard as the bullet strikes the target.

Now, recall that bullet's have two types of energy. First, they have potential energy in the form of their mass and velocity. Energy is the ability to do work. Work is required to move and damage tissue. Therefore, more energy would seem to demonstrate the ability to do more damage to tissue. But in truth, this is dependent on how the bullet transforms potential energy into kinetic energy. In order to do this, a bullet must lose either or both velocity and/or mass. How it does this is dependent on the bullet's construction.

Lastly, we must remember that all spitzer (pointed) bullets are heavier in the base than in the nose. As a result, their center of gravity is located more towards the rear of the bullet. This means they all have a natural tendency to fly base forward. This is why rifles are given rifling. Putting a spin on the bullet stabilizes the bullet like a top. This is also why longer bullets require faster twist rates. However, like a top, the bullet is only stable as long as it stays over a certain rotational velocity. The rotational velocity required for a bullet to remain stable depends on the density of the medium it is passing through. Even differences in the density of air can have a dramatic effect. For example, a bullet that is stable in a warmer atmosphere may not be stable in a cold, humid atmosphere because colder air is more dense than warm air. Likewise, a bullet stable in air typically becomes unstable in tissue, because tissue is more dense than air. This means that all pointed bullets have a tendency to flip around and travel base forward once they enter tissue. The difference is that some bullets exhibit this tendency to yaw and tumble more readily than others. This is because some bullets are more base heavy than others. For example, the original M43 ball round for the 7.62x39 was known to penetrate very well, but remained stable for often more than 8 inches of penetration in tissue before beginning to yaw. So it really created wounds that were in many cases indistinguishable from a .38 caliber handgun. The Yugos noticed this and designed the M67 ball round for the same cartridge to remedy it. The round looks like a standard FMJ. However, it has a large air pocket in the forward 1/3 of the nose. This made the bullet more base heavy. Now this would normally require a faster twist rate, but it just so happens that the Russians thought ahead, and the AK already has a very fast one-in-nine-point-something twist rate that readily stabilized the new projectile. The result was a bullet that often began tumbling within the first 3 or 4 inches of tissue. The Russians took note and incorporated a similar concept when the adopted the 5.45mm round.

Tumbling increases wounding effect because it displaces more tissue when the bullet is sideways. The more area a bullet has exposed to tissue, the more damage it does. Why? Because more exposed area means more resistance. This in turn means the bullet loses more velocity than it does when traveling point forward. And losing velocity turns potential energy into kinetic energy.

There are other ways this is done. The most popular is expansion.

Recall that the target hits the bullet as hard as the bullet hits the target. Equal and opposite. This means that more energy will always, without fail, in every case, with no exception be more likely to cause a bullet to deform, regardless of the bullet's construction. Take any bullet, and it is more likely to expand the faster you push it. So it is therefore impossible to push a bullet so fast that it "zips right through" a target without expanding. A bullet may pass through a target without expanding, but this is due to the bullet being of too "heavy" of construction to expand. Pushing it faster will always make it more likely to expand. Always. In this universe for as long as Newtons Laws are applied to the world around us, this will be true. However, some bullets are made to expand more readily than others. Most hunting bullets are designed to expand, though some again more readily than others depending on the game they were intended for. Similarly, defensive rifle and handgun ammunition is designed to expand readily on thinned skinned "game" like humans. This is done usually by making the jacket on the nose of the projectile thinner and adding a softer lead core. Polymer tips or noses of exposed lead are often used for the same reason. The jacket gets progressively thicker towards the base to control expansion as the bullet peels backwards.

So a Jacket Soft Point hunting bullet hits the shoulder of a deer at near muzzle velocity of say, 2700 fps. This bullet is designed to expand and maintain most of its mass (more on that in a second), and penetrate deeply on deer sized game within a velocity threshold of say 2000 to 3000 fps. So at 2700 fps, it expands readily. The resistance provided by the tissue causes the bullet to collapse like a crushed soda can. This deformation is evidence of velocity being lost to do work that is required to change the shape of the bullet and displace and damage tissue. As the nose of the bullet expands, it has a parachute effect which increases drag. This drag sheds velocity, which is turned from potential energy into kinetic energy.

If you've been paying attention then right now you are asking why the hunting bullet, being pointed, doesn't just tumble like a military style ball round? This is because the bullet becomes shorter as it expands. This moves more mass to the rear, which largely counterbalances the bullet's tendency to yaw and tumble. Still, it isn't uncommon to see wound tracks that curve, or to even see the occasional key-holing exit wound as evidence of the bullet tumbling.

You might also rightly be gathering that expansion is the enemy of penetration. More expansion means less velocity remains for forward travel, and therefore, less penetration. This observation would also be correct, and shows the importance of matching bullet construction to the job at hand. Expansion damages more tissue, but this does little good if it does not occur deep enough to damage vital structures. Therefore you must find a bullet that penetrates deeply enough to reach the vital regardless of whether it encounters an oblique angle and/or a shoulder joint, while still exhibiting as much expansion as possible inside the chest cavity of the target.

Now then. Push that same bullet at 3200 fps. Let's say it is a conventional Sierra GameKing SPBT. It does well at typical .30-06 velocities, such as the 2700 fps used in the first example, but was not designed to accommodate the velocities of the latest beltless magnums. So if you push the bullet at 3200 fps from a Remington Ultra Mag, the bullet expands violently. The thickness of the jacket and the softness of the core were never intended to deal with these energies. The bullet compresses on itself, flattens rapidly, and tears apart, fragmenting into a dozen small pieces. This is how you get fragmentation. Fragmentation is just extreme expansion. It happens when the bullet is pushed beyond the limits it can remain structurally intact. It is the most extreme form of energy transfer. The smaller pieces have less mass, and therefore less momentum. They lose velocity faster, and thus, rapidly transfer all potential energy into kinetic energy. In some cases, when this occurs deep enough in the thoratic cavity, the results can be devastating. However, in this case, the round blows up on the shoulder of the deer. Most of the muscle tissue and ligaments are turned to jelly. The scapula is shattered. But few of the bone fragments and none of the bullet fragments make it deep enough into the chest cavity to damage vital structures such as the lung and heart. The animal jolts, and twirls at the impact, then jumps over the side of the bank and is last heard rather than seen crashing through the foliage. Thus, more energy is not always a good thing, and our hunter learns a valuable lesson--bullet construction matters.

Let's consider a final example before this long-winded reply is concluded, leaving you more confused than ever.

The 5.56 NATO round is often used as an example of a round that fragments. But let's consider why. The 62 gr M855 ball round has a cannelure. This simply means the bullet has a series of skivvies or indents in the jacket, oriented up and down on the bullet with its direction of travel, in order to allow for more surface area to engage the inside of the neck of the case when it is crimped. This is typically done to prevent the bullet from being pushed back into the case, when can drastically increase pressures, and is especially important in self-loading firearms which can have violent chambering cycles. Bullets without cannelures may not provide enough crimp area to prevent the bullet from being pushed back into the case as it is shoved into the feed ramp and up into the chamber.

Now, the bullet is a FMJ of fairly tough construction. It isn't designed to readily expand. It is oriented more towards penetration. However, being a spitzer bullet, it does have a tendency to yaw and tumble. This tendency isn't as great as say, the Russian's 5.45mm ball round, but it still exists. At higher velocities, as the M855 round tumbles, it tears in half along the cannelure, which also happens to weaken the jacket. It is like the perferated edges on the old printer paper. While tumbling, the bullet is torn in half, and then either continues in two seperate wound tracts or continues to fragment.

Stay with me, this is where it gets complicated...

Recall that expansion is more likely as energy increases. However, bullets shed velocity due to air resistance in flight, and as this occurs, the bullet's lose energy. Therefore, bullets are always less likely to expand the farther down range they get. The same can be said about fragmentation. The M855 round expands consistently at 2700 fps, sometimes at 2500 fps, but almost never below that velocity threshold. This means that even from an M16, fragmentation is unreliable beyond 150 to 160 yards.

However, a bullet's yawing effect is not as reliant on velocity. In fact, though it loses rotational velocity at a slower rate than linear velocity, it still loses rotational velocity as it travels down range. This means it loses stability, although relatively slowly, as it travels downrange and may, because of this, increase its tendency to yaw and tumble in tissue.

Have I lost you yet

So the M855 is likely to be more effective inside the range at which it retains sufficent energy to fragment than a round that simply tumbles, such as the 5.45mm. However, beyond this range, while it still retains the tendency to tumble, it was not designed to do so as readily as the 5.45mm round. Without fragmentation, the M855 isn't as effective as the 5.45mm because it isn't as long--it therefore displaces less tissue when tumbling--and it takes much longer for it to tumble.

To answer your question then, expansion and fragmentation can be much more effective than tumbling or yawing, but they are less reliable because they are more reliant on impact energy.

Holy crap that got long

 

[stubbicatt]

So, considering the example of the 7N1 round, which is of 3 piece design, again to tumble readily in flesh, wouldn't that round create or tend to create a larger wound channel than say, a similar 150 grain Sierra Game King, since the portion of the bullet that acts upon the medium is the side or length dimension versus the expanded nose dimension, and the 7N1 bullet is pretty darned long? Stated in other words, the hypothetical 1.25" long 30 caliber bullet traveling sideways makes a 1.25" sectional cut through the medium, where the mushrooming bullet cuts a .5" hole through the same medium.

Wouldn't hydrostatic shock be roughly equivalent given two projectiles of the same shape and size passing through the same hypothetical wound channel? Would hydrostatic shock be greater or less for the mushrooming projectile vs the keyholing projectile?

If yaw is less dependant upon velocity than is mushrooming, why isn't this modality considered in the manufacture of hunting bullets?

I guess if you rule out fragmentation as a reliable or desireable feature of a bullet, that leaves us either mushrooming or tumbling. If hydrostatic shock stays relative, and my intuition suggests that it is relative or similar between a mushrooming and a yawing bullet, then what is left for consideration in the lethality of the projectile is the size of the permanent wound channel, right?

If yaw more reliably creates a larger wound channel over a wider spread of velocities, it seems to me that the modality of the yaw would be preferred over the less predictable or reliable modality of mushrooming or expansion, which is more dependant upon impact velocity.

Hunting prairie dogs with FMJ ammunition will certainly kill the pd's, but is also likely to produce ricochets. Not many farmers/ranchers want to have ricocheting bullets whistling past their ears, into their livestock, or buildings/equipment. Bullets like V-Max's aren't likely to ricochet - I've had them come apart on grass on the way to a partly hidden pd.

Thanks LarryE. This is good advice. Thankfully the area where we shoot the dogs has none of these ear whistling, livestock or building equipment potentialities. I guess too I must be sold defective Vmax bullets as from time to time I can hear the characteristic whine of a ricochet even using Vmax's. It is not as frequent an occurrance, however.

 

[cjanak]

Related links:

The High Road on Hydrostatic/Hydrodynamic Shock
Chuck Hawks on Killing Power
Chuck Hawks on The Rifle Cartridge Killing Power Formula.
Chuck Hawks Hunting Bullet Guide Part I
Chuck Hawks Hunting Bullet Guide Part II

 

[Jst1mr]

A bullet in a state of yaw travels through the medium in an unpredictable manner...for hunting, you want your bullet to follow a known path through a select area, not wander around through the internals.

 

[Art Eatman]

I'm sorta simple-minded empirical. I've found that an '06 will generally blow on through, out to around 350 or 400 yards, anyway. My .243 loads tend to make a double-handful of mush inside a deer's chest cavity, and on a poor old coyote will carry the mush out the far side.

.223 to .220 Swift tends to just make big messes out of prairie dogs and jackrabbits. Red mist.

I dunno as how I've ever seen any evidence of tumbling with the loads I use.