# Value of rate of twist on hitting power of a handgun



## eddiebritz (Nov 16, 2011)

Hi All,

There is currently a hot argument raging amongst our shooting club members about the value (effect on "hitting power") of the rate twist (bullet spin) on the "hitting power"of a typical handgun.

Some mebers argue that the very high spinning rate of a bullet has n very damaging effect of the body tissue it hits and passes through. According to them the rate of twist plays a major role in determining the "hitting power" of a handgun bullet.

Other members argue that the rate of twist has very little if any role to play (other than stabilising the bullet for accuracy) in the "hitting power" of a handgun bullet. According to then a typical handgun bullet only do 1 rotation (spin) for every 14 - 18 inches (depending on the particular gun's rate of twist) of distance it travels so if it hits and passes through a human body (about 12 inches deep) the bullet will not even complete one spin while it is in the body - it is hardly likely that a one or less rotation of the bullet in the body is going to be very spectacular of have much effect on it's "hitting power". 

The opponents then point out that the typical bullet spins at a rate of up to 50,000 rpm in the typical 9mm pistol and that such a tremendous spinning speed of an object in flesh cause significant shock and damage so it must play a major in the gun's "hitting power".

The counter argument is that a bullet does not stay in the body for one minute while passing through but more likely stays for less than 0.06 of a second. This short time don't give the bullet enough time do complete it's 50,000 rotations in the body - it would hardly complete one rotation in that short time. 

I would appreciate the views and explanations of you who are likely much better terminal balistic experts than me.

Regards,

Eddie


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## Packard (Aug 24, 2010)

Everything I've ever read or heard indicates that the rate of twist is specified to improve accuracy. I don't believe it has any other influence on the projectile.

Unless you are shooting drill bits I don't think the rate of twist will affect the target in terms of damage.


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## DanP_from_AZ (May 8, 2009)

eddiebritz said:


> . . . There is currently a hot argument raging amongst our shooting club members about the value (effect on "hitting power") of the rate twist (bullet spin) on the "hitting power"of a typical handgun.
> 
> . . . 1 rotation (spin) for every 14 - 18 inches (depending on the particular gun's rate of twist) of distance it travels so if it hits and passes through a human body (about 12 inches deep) the bullet will not even complete one spin while it is in the body - it is hardly likely that a one or less rotation of the bullet in the body is going to be very spectacular of have much effect on it's "hitting power".
> 
> ...


I looked around my "Man Cave", and for whatever reason, there were NO rocket scientists present.
So, you will have to consider my views as a lowly mechanical engineer (retired).
And further in my favor (and maybe to your sorrow), I have the ability to touch-type as fast as I can think. 
Uhhh, I'm not sure if that is a feature or a bug. Does that mean really fast typing, or . . . maybe it's thinking at 7.6 words per minute ?
In my favor, I HAVE stayed in a Holiday Inn Express. But . . . not last night.

As usual, some people refuse to believe that the Newton's laws of physics cannot be violated.
(OK, they are REALLY difficult to violate, like up around and right at the speed of light - as in E = M x Csquared).

In person, I like to point out these people are being totally stupid, and see if I can explain why. IF they are capable of comprehending.
This approach is seldom "well received".

OF COURSE the bullet is not a spinning scythe (or propeller, or whatever) slicing and dicing flesh, human or otherwise.
I'm not even going to calculate if a "standard" bullet might actually be spinning at 50,000 RPM (Revolutions per Minute).
Assume that RPM "might" be correct. It could only chew up flesh if you could magically slow it down enough so that it took
a LOT OF TIME passing through someone's body (hopefully a perp). Like if it took "the magic minute" to traverse the body
then it might cut through like a buzz saw moving sideways. Assuming of course, that just before it pushed through the top
layer of skin, it magically deployed those little "flower petal arms" you see on retrieved self-defense bullets. On good ones, anyway.

So, let's think about what we have with this two opposing "scientific hypotheses". Now WHAT do we have.

First case a bullet that rotates once in every "twist whatever" like every 10-20 inches. Let's use a hypothetical "good"
.40 S & W. Maybe expands to .60 inches as it punches through the body. The bullet has a "shock effect" on soft tissue.
Think of "that wave" you see in high-speed movies of bullets impacting that "wonderful simulation of human tissue", the
10% ballastic gelatin (unflavored Jello). Now look down at your chest. Or even better, down at your beer belly. Does it look
like that gelatin ? OK, sorry about that. Your chest does not. Your beer belly approximates a long block of Jello. Just taller and wider.

What I'm saying, is a good expanding bullet has increased the diameter "some". And because what is "working on the perp"
is the area of the bullet, a bit of diameter expansion can help quite a bit. As always, Area = Pi x Diameter Squared.
Uh, maybe I should look that up. I'll just wing it. Yep, I think Area = 4 x Pi x Radius Squared. Well, let's just go with that flow. 
Anyway, increasing the diameter by expansion helps dissipate more energy in the perp by "some" worthwhile amount. 
And laying more energy inside your chest cavity is a good thing for a bullet. Oops, I mean inside THEIR chest.

Second, after that long-winded deal, the spinning propeller theory is easy. So, say the .40 caliber guy magically springs the
little prop blades out to .60 diameter. If they could spin it 50 thousand times while passing through a body, they would have
the same effect of a flat disk of the same diameter. Think of it as "how much flesh bite can each prop turn eat up ? Divide the
15 inch body thickness by 50,000. Now that is a pretty small bite per revolution.

Oops, I forgot. Scratch that. This "spinning propeller" making significant slices at real bullet speed is impossible because the
"true revolutions" it can make are spread across the time it took to travel through the body. Even if it goes from 900 - 1500
feet per second to zero, stopping in the body, that time is all the time it has to rotate. And it ain't going to be much rotation.
As many of my most disliked lofty Professors loved to say, "the proof is left to the student". And "Turn yours in next class".

So, now go back to your club, and announce you have been to the mountain. And the "Guru of All Moving Things" has spoken.
And he pronounced, with a suitably dark thundercloud background, and an occasional lightning bolt illuminating his grave and craggy visage,
"You Propeller Heads are Filled to Your Eyeballs with an Extremely Excessive Amount of Bovine Excrement". 

Postscript:
Actually, in all seriousness (no, really) the "inhuman flesh-devoring spinning propellor of death" argument was used "back when" to kill the
Winchester "Black Talon" self-defense load. Just looking at their advertisement with those evil "petals of death" spiralling out of that black-coated
bullet was enough to scare the living 'bejeus out of every left liberal enemy of the Second Amendent in the entire continental United States.

Winchester saved the cost of the black paint, paid the cost of new bullet box printing, and put some bucks in a kinder, gentler ad campaign.
I still have a carefully preserved and totally unused box of 9mm Black Talons in my gun safe.


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## Packard (Aug 24, 2010)

DanP_from_AZ said:


> I looked around my "Man Cave", and for whatever reason, there were NO rocket scientists present.
> So, you will have to consider my views as a lowly mechanical engineer (retired).
> And further in my favor (and maybe to your sorrow), I have the ability to touch-type as fast as I can think.
> Uhhh, I'm not sure if that is a feature or a bug. Does that mean really fast typing, or . . . maybe it's thinking at 7.6 words per minute ?
> ...


Dear DanP,

So let's see if I can paraphrase your response to the question: Does the rate of twist in rifling affect stopping power?

Answer: No.

Please affirm that my paraphrase is essentially correct.

Regards,

Packard


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## HK Dan (Dec 22, 2010)

<chuckles> I nominate Dan P as the Director of Complicated Solutions for the site. Any seconds?

Think about it--the bullet is spinning within it'[s own diameter. The spin adds nothing to the effect of the bullet. Ask your buddies how it is that the plain round balls fired by muskets did so much damage with no spin at all. Ask them why knives are deadlier than bullets and there is no spin what so ever. (85 % of handgun victims survive their wound. 65% of knife victims survive theirs).

Were that true, that spin rate increases damage, would the firearms industry not realize this and would not every handgun fire with a 1:5" spin rate instead of a 1:19? Instead they are made with a spin rate that best compliments the 'normal' bullet that they will fire (for accuracy).

I don't believe that spin rate effects the damage that a bullet does.

Dan


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## MLB (Oct 4, 2006)

I nominate Packard as the Forum "Master of Laconic Posts", a title with length disproportionate to its qualifications.

(and a quick second of his "no" on the spin effect too.)


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## DanP_from_AZ (May 8, 2009)

Packard said:


> . . . Please affirm that my paraphrase is essentially correct. . .


Affirmed. :mrgreen:


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