Twist rate vs killing power.

[jb6.5]

I watched a dvd that barnes gives out. From what they claim, and show on a super slow motion film the bullets rotation does in fact cause trauma. Seems like the more spin the more it would tare up. The ballistic jell showed swirls spiraling off the bullet from the rotation through the whole block. Pretty cool to watch.

[Geo_Erudite]

Numbers is what numbers is.......but those numbers don't pass the "smell test." If barrel twist had that big of an effect on down range energy, I would think I would have read a whole bunch about the subject in all of the books, articles, and gun rags I've read in the last ten years.

There may be a difference on paper, but the real difference in the field is too small to measure.

Fair enough, I understand your point of view.

[JackinSD]

I watched a dvd that barnes gives out. From what they claim, and show on a super slow motion film the bullets rotation does in fact cause trauma. Seems like the more spin the more it would tare up. The ballistic jell showed swirls spiraling off the bullet from the rotation through the whole block. Pretty cool to watch.

What you are seeing is a very small percentage of the actual energy released within the animal, in the 1-2% area. No matter how fast you twist the bullet out of a normal rifle barrel.

Yes, you get more energy with a faster twist. However, the rpm of the bullet (energy) within a given caliber at various twist rates have an almost nonexistent difference.

More energy? Yes. Enough to see a difference? No.

[Geo_Erudite]

Really this comes down to two points of view, which neither is incorrect. One side of the debate you have the reduced complexity crowd, which realizes it is the basic components that describe what is going on. Jack is probably correct that 98% of what is seen can be explained by linear velocity and energy at the point of impact that carries through as the bullet moves through the animal. The other side of the debate realizes that the other 2% that isn't explained is a form of deterministic chaos. This side of the debate sees that the 2% not explained can have huge ramifications that escalates the amount of "damage" done (e.g. a bullet with a faster twist rate and higher energy rips an artery in an animal that a slower twist rate and lower energy would not rip).

[JackinSD]

Really this comes down to two points of view, which neither is incorrect. One side of the debate you have the reduced complexity crowd, which realizes it is the basic components that describe what is going on. Jack is probably correct that 98% of what is seen can be explained by linear velocity and energy at the point of impact that carries through as the bullet moves through the animal. The other side of the debate realizes that the other 2% that isn't explained is a form of deterministic chaos. This side of the debate sees that the 2% not explained can have huge ramifications that escalates the amount of "damage" done (e.g. a bullet with a faster twist rate and higher energy rips an artery in an animal that a slower twist rate and lower energy would not rip).

You could well be right on that also.

[TC260]

Kinetic Energy:

.5 * mass * angular velocity ^ 2

Where did you get this equation from? It doesn't make sense. The resulting units are Kg/s^2 which doesn't equate to anything. The equation for rotational energy I'm familiar with is .5*moment of inertia*angular velocity^2. Even still I don't think rotational energy is useful here. Centrifugal force I think is the property we should be looking at. In some cases it's obviously a strong enough force to rip the bullet apart in mid flight.

I watched a dvd that barnes gives out. From what they claim, and show on a super slow motion film the bullets rotation does in fact cause trauma. Seems like the more spin the more it would tare up. The ballistic jell showed swirls spiraling off the bullet from the rotation through the whole block. Pretty cool to watch.

Is that the same video where they talk about the bullet "augering" it's way through the medium?

[Geo_Erudite]

Where did you get this equation from? It doesn't make sense. The resulting units are Kg/s^2 which doesn't equate to anything. The equation for rotational energy I'm familiar with is .5*moment of inertia*angular velocity^2. Even still I don't think rotational energy is useful here. Centrifugal force I think is the property we should be looking at. In some cases it's obviously a strong enough force to rip the bullet apart in mid flight.

Here, but you can use any unit you want in the equation as long as it is the same consistent unit.

I think that torque makes better sense, but I don't have the table in front of me to calculate those values.

[slugslinger]

I'll agree with squirrelsniper; of all that factors that affect wound channel, I suspect rpm at impact is down a few on the list (unless of course the bullet is actually unstable/tumbling at impact). FPS, energy, bullet weight, bullet type/shape/composition, and especially shot placement and animal bulk/density would be more critical. RPM is a factor, yes, but not the predominant one . . . but evaluating ALL the factors is what makes it fun, right!!

[TC260]

In the link provided, (1/2)mv^2 is the equation for linear kinetic energy + (1/2)Iw^2 which is the equation for rotational energy where I = moment of inertia, w = "omega" which is angular velocity. For "I" you'd use something like what's on this list here http://en.wikipedia.org/wiki/List_of_moments_of_inertia

[gerard488]

Someone please correct me if I1m wrong but here`s what I came up with on twist rate:
Any bullet leaving a 1:12 twist barrel at 2800 ft/sec is spinning at a rate of 2800 revolutions/second which equals 168000 RPM
Any bullet leaving a 1:8 twist barrel at 2800 ft/sec is spinning at a rate of 4200 revolutions/second which equals 252000RPM
Another way is to use the formula for bullet rpm which is MV x 720/twist rate in inches( 2800 x 720 /12 = 1680000 )
That is a difference of 84000 rpm at the muzzle. Enough to make a difference? Maybe

[jb6.5]

I think rpms have a good bit to do with the damage a bullet does. Several post mentioned ke, but I know some bullets aren't made to be pushed above a certain fps, if so they will come apart. Its not the fps its the rpms. I'm not an expert on ke and all the factors that goes along with it. I can say I've shot alot of critters and took notice to what bullet has done what. Something makes the creedmoor cause more damage than most guns we've used.

[big honkin jeep]

You guys can do all the math in the world there is a huge difference between bullet performance which can be calculated to a tee and putting down a game animal which is anything but absolute. Too many things to consider like the size of the animal and the construction of the animal. They all have different thickness of hide and bone and each organ has it's own characteristics as well. Throw in the different constitution (will to live and or flee) of each animal and you have something that numbers don't have an answer for. Often times a bone hit by even a comparatively small bullet of any type construction will turn into lots of high velocity bone shrapnel and the wound channel will look like it was done by a hand grenade.
I really think the fundamentals of proper caliber and shot placement are what gives you the best odds, and would use whatever twist stabilizes the bullet and provides the most accurate shot placement.
Just another .02

[TC260]

I really think the fundamentals of proper caliber and shot placement are what gives you the best odds,

Rereading the thread, I don't see anyone proposing anything contrary to that. It's just some speculation as to why a medium sized round (6.5 CM) seems to have outsized performance on game. A little basic physics just adds some information to the discussion. Now if we'd broken down the bullet shape and integrated it to actually calculate centrifugal force to a tee then I'd agree that "the math" had gone too far

[stangfish]

The earth does not spin faster at the equator than it does at the polls. Faster twist rates do more damage because the bullets act like saws after they open.

[jb6.5]

Yep

[big honkin jeep]

The earth does not spin faster at the equator than it does at the polls. Faster twist rates do more damage because the bullets act like saws after they open.

Nope they act like bullets. With the hydrostatic shock wound channel being so much larger than the expanded bullet diameter I am convinced any "sawing" effect is relegated to chewing up tissue that has already been reduced to purple mush by the bullet doing its job.

[WuzYoungOnceToo]

The earth does not spin faster at the equator than it does at the polls.

I'm not sure what it has to do with the subject at hand, but that claim depends on how you're using the word "faster". A person standing on the equator is certainly traveling around the Earth's axis at a much higher velocity than he/she would be while standing at/near one of the poles.

Faster twist rates do more damage because the bullets act like saws after they open.

Uhm....no.

[thomae]

I was ignoring most of this thread, but it looks like it is just starting to get interesting.

[stangfish]

Wuzyoung,

The earth does not spin faster at the equator than it does at the polls.

This was a response to this

There is a thing called angular velocity, which could explain what is going on. In simple terms it explains why the Earth spins faster at the Equator and slower at the North and South Poles.

How do you know that an expanded bullet doesn't act like a saw. I don't believe in hydraulic shock, or Santa or tooth fairies....

As far as spinnng speed I think everywhere on the planet earth is rotatating at 1 revolution per day. Now surface speed is is another story.

[Geo_Erudite]

As far as spinnng speed I think everywhere on the planet earth is rotatating at 1 revolution per day. Now surface speed is is another story.

I may have incorrectly stated angular velocity, when I should have stated linear velocity. In the end though, the earths circumference at the equator is 24,902 miles, while the circumference of the earth at the poles is 0 miles. It takes 24 hours for the earth to rotate at either point.

Euator: 24902/24= 1,038 mph

Pole: (24902*[cos(90)])/24= 0 mph

[WuzYoungOnceToo]

Wuzyoung,

This was a response to this

How do you know that an expanded bullet doesn't act like a saw.

Because we know what the approximate rate of rotation is for bullets, and thanks to things like high-speed photography and other nifty technologies we have a pretty good understanding of the behavior of bullets when they travel through the target...and neither things suggest any saw-like effects on tissue.

I don't believe in hydraulic shock, or Santa or tooth fairies....

There's a fair amount of physical evidence and peer-reviewed research that support the theory of hydrostatic shock. Not so much for Santa or the tooth fairies.

As far as spinnng speed I think everywhere on the planet earth is rotatating at 1 revolution per day. Now surface speed is is another story.

Which is why I said it depends on how you're using the word "speed". Had you included in your previous post a quote of what it was you were responding to then that question would have been answered.

[stangfish]

Waz, I am a troll in this thread. I personaly don't believe most of what I have written on this post. I am sorry for taking you down this path, I am in the hospital on Morphine and have nothing better to do.

[stangfish]

I may have incorrectly stated angular velocity, when I should have stated linear velocity. In the end though, the earths circumference at the equator is 24,902 miles, while the circumference of the earth at the poles is 0 miles. It takes 24 hours for the earth to rotate at either point.

Euator: 24902/24= 1,038 mph

Pole: (24902/[cos(90)]/24= 0 mph

you are correct and I think we all knew what you ment. I just needed a reason to troll.

However, I do believe that the pole ocsilates somewhat so I am not sure Zero is the correct answer either. At least not for the magnetic pole.

[thomae]

There's a fair amount of physical evidence and peer-reviewed research that support the theory of hydrostatic shock. Not so much for Santa or the tooth fairies.

WHAT!?!?
Have you ever seen the face of a child light up on Christmas morning? In my book, that's plenty of proof that Santa exists. You might not be able to fingerprint him, but he exists, nonetheless. Where does he live? You never know...it might be right in your own heart. If you truly don't believe that Santa exists, I feel sorry for you.
[/rant off]


PS:
1. The magnetic poles move around...that's why magnetic variation changes on maps from time to time.
2. The physical poles move as well because the earth doesn't spin perfectly, it wobbles just a bit. The technical term is "nutation" and when you are attempting to do precise celestial navigation (a three-star fix) it has to be taken into account in order to obtain an accurate position.
3. None of that will affect your shooting ability in any measurable fashion.

[stangfish]

Thanks for the input Thomae, Now about that sawtooth killing action of the bullet chewing up the pulverized bloodshot meat.....