I found this info while hunting in a old handloader's digest. Writer is Roy F. Dunlap.

" Know how fast a bullet spins? Guess. Guess again. Give up? Now hear this: a 30-06 150-grain bullet fired a 2970 fps from a 10-in. twist barrel has a rotational speed of 213,848 revolutions per minute. Over 3500 revolutions per second! Even a 22 Long Rifle bullet, fired at 1120fps through a 16-in twist barrel has over 50,000RPM. Bullets need to be uniform in every way." Roy F. Dunlap, Handloader's Digest, tenth edition, DBI Books

Cool eh? And I thought the spin on the political forum was something!

Yep, and a 55/.223 through one of those 1-7" barrels at 3300 fps is doing 339,428 RPM. And you thought that the little Porsche engines could wind?

So let me try to figure this out; if your 22lr rotates once every 16 inches, fired at a target 150 feet away, it will rotate 112.5 times before hitting the target. That ain't so much.

Uh-huh, BUT they still only make one revolution per 10" or whatever the twist rate is!

I would tend to think that as the external Forces contact the bullet that the 1:10 and so forth get thrown out the window. Especially w/ fast velocity, the only time it will spin a set amount of times is when it's in the barrel. I would imagine the spin slows down from the data I've seen. What do you fellas think?

Reloader

One of the bullet manufacturers tested the spin rate degredation and they found that spin slowed very little when compared to velocity and seemed to only change drastically when something solid was hit.

quote:

Originally posted by Fjold:
One of the bullet manufacturers tested the spin rate degredation and they found that spin slowed very little when compared to velocity and seemed to only change drastically when something solid was hit.

Foreward velocity and rotation are two independent and separate things.

The forces retarding foreward motion are enormous and the forces retarding rotation are almost nonexistant.

It's only reasonable that rotation is not deterred as the velocity slows.

Anyone that spent money testing this probably needs to be seated in an elimentary physics class.

As a curiosity comment, if one shoots a bullet into the sky 85 deg from the horizontal at 3,000'/sec and 250,000 RPMs the bullet will land again on the earth not too far from where it was fired but at a velocity of about -350'/sec and maybe 150,000 RPM and, of course, will hit heel first and not point first.

The numbers of pure estimate and not calculated only to illustrate the point.

quote:

Originally posted by vapodog:

quote:

Originally posted by Fjold:
One of the bullet manufacturers tested the spin rate degredation and they found that spin slowed very little when compared to velocity and seemed to only change drastically when something solid was hit.

Foreward velocity and rotation are two independent and separate things.

The forces retarding foreward motion are enormous and the forces retarding rotation are almost nonexistant.

It's only reasonable that rotation is not deterred as the velocity slows.

Anyone that spent money testing this probably needs to be seated in an elimentary physics class.

As a curiosity comment, if one shoots a bullet into the sky 85 deg from the horizontal at 3,000'/sec and 250,000 RPMs the bullet will land again on the earth not too far from where it was fired but at a velocity of about -350'/sec and maybe 150,000 RPM and, of course, will hit heel first and not point first.

The numbers of pure estimate and not calculated only to illustrate the point.

I wish I could remember where I saw the article and which manufacturer it was because it was a great read.

The rotational velocity testing was done when the manufacturer received bad field reports of their bullet's terminal performance at long ranges. To simulate the field conditions they tried to load the bullets to a lower muzzle velocity on a short range instead of full velocity at long ranges. They saw drastically difference terminal performance of the bullets than what they had seen shooting at long range. They initially though that it might be due to the reduced rotational velocity. That lead them to test for degradation of the rotational velocity and its effects on terminal performance.

The forces imparted on the front of the bullet have an impact on the forces of the bullet spining much like that of frictional forces.

There are many variables that could impact the spin of the bullets such as moisture content in the air for instance which in essence sort of puts a frictional component in the equation.

As the bullet slows it slows because of the forces opposing it's movement in a constant direction. Forces are also slowing the rotational speed. As the bullet slows so does the spin. I agree that it is not even close to the same amount speed wise but, they do both slow.

We get into some interesting discussions don't we.

Reloader

quote:

Originally posted by Wink:
So let me try to figure this out; if your 22lr rotates once every 16 inches, fired at a target 150 feet away, it will rotate 112.5 times before hitting the target. That ain't so much.

No, it will rotate several more times than that. This is because (as the above discussion has pointed out) the rotational spin slows much less quickly than the forward velocity, therefore any bullet fired from a rifled barrel will reach its target after spinning more times than the 1 turn for each unit of rifling twist.

Carried to the extreme, a bullet very near its maximum range will be making one full rotation during only a small fraction of the forward motion that represents the rate of barrel twist. In fact, when it has reached its maximum forward range and is falling straight down, that sucker is still spinning.

What's amazing is how little energy it takes to set it spinning at this high rate. If the energy were significant, your rifle would try to torque out of your hands upon firing. As it is, have you ever been able to tell the difference in left-hand vs. right-hand twist by detecting the difference in torque?

After all Fellas... how do you think they make those beautiful mushrooms!

.

quote:

Originally posted by ALF:
Vapodog:

If the bullet that is doing say 2500 fps ( linear velcoity )and 220,000 rpm comes to a dead stop in the target after penetrating say 24 inches it means that both linear velocity and rotational velocity comes to a dead stop.

Yes...we're in sync here....

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Whilst I have seen it claimed that linear velocity degradation happens faster than rotational velocity degradation if total target time from impact to a dead stop is .4 microseconds then the rate over the .4 microseconds would be faster for the one with the geatest value. ( But then you would have to rework the two velocties to the same units to compare. )

Sorry ALF...ya lost me there....

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In the time it takes to come to a stop the projectile would still only have done 2 or maybe 3 revolutions before stopping.

Agreed

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It does not spin like a top in one place in the target ????? So the bullet does not act like a buzz saw in the target.

I think this is true as well.

I'm not sure what the point is however...it wasn't stated by myself or anyone that the bullet acted like a buzz saw in the trauma channel.....Help me out here Alf...what are we saying....are we disagreeing with something that has been posted?

I think conservation of energy is the issue to be reconned with here.....the energy in rotation is small compared to the energy in linear motion. The amount of resistance needed to stop it is therefore small and the forces causing the bullet to upset and mushroom will take it's toll on rotation. Further the rotation will be disrupted by the expansion of the OD of the mushroomed bullet....much like a figureskater spinns faster with her arms overhead and slower with her arms outstretched.....same with a centrifugal clutch.

However you and I do not disagree at all that the does not sit in the trauma channel and spin like a top for a second or so....or that the bullet acts like a drill bit or a screw.

The game IMO changes dramatically when the bullet leaves air and enters flesh and bone.

I remember being 5 years old and asking what was being calculated on the big white tablet.

"The reaction on the barrel from bullet twist"

Now 50 years later, I can see that just figuring out the formula and calculating the final bullet spin should be much easier.

[12"/foot] [60 seconds per minute] [feet per second of muzzle velocity] / [inches per turn of barrel twist] = bullet r.p.m. [revolutions per minute]

12 60 2970/10 = 213,840 r.p.m.


Well Roy was close, anyway.

More numbers:

213,840 RPM

For a 30.06 bullet:
213,840 Rev/Min X Pi X .308" = 206,913 inches per minute, rim speed

Or 287 fps

Stonecreek, I don't understand your explanation. How can a bullet rotate more times than the imparted rotation produced by the rifling twist? If in the example I used the rifling twist is 1:16, then how can it rotate faster than once every 16 inches? 150 feet is equal to 1,800 inches. In covering that distance it will rotate 1800 divided by 16 equals 112.5 rotations. That assumes that the rotation won't be slowed by any forces at all. But rotating faster than that? You've lost me.

quote:

Originally posted by Stonecreek:
As it is, have you ever been able to tell the difference in left-hand vs. right-hand twist by detecting the difference in torque?

Yes.

quote:

Originally posted by Wink:
Stonecreek, I don't understand your explanation. How can a bullet rotate more times than the imparted rotation produced by the rifling twist? If in the example I used the rifling twist is 1:16, then how can it rotate faster than once every 16 inches? 150 feet is equal to 1,800 inches. In covering that distance it will rotate 1800 divided by 16 equals 112.5 rotations. That assumes that the rotation won't be slowed by any forces at all. But rotating faster then that? You've lost me.

I'll let stonecreek provide the explanation.....but FWIW I agree with him....strange???...nope it's not at all.

OK, I think I'm catching on. It's rotational spin will basically remain constant once set in motion, no matter what its forward movement. Am I on the right track? I would guess that at 150 ft and the "several more rotations" would be minimal.

quote:

Am I on the right track?

yup

quote:

Originally posted by Jon A:

quote:

Originally posted by Stonecreek:
As it is, have you ever been able to tell the difference in left-hand vs. right-hand twist by detecting the difference in torque?

Yes.

Not necessarily right vs left but the torque imparted to the gun by forcing the bullet down the rifling is especially noticable in a big-bore, light-weight handgun. A .475 Lin. in a Casull single action tries to twist out of my hand. The torque as quite pronounced. In a heavy handgun in .44mag I don't even notice the torque, but it's obviously still there.

quote:

As a curiosity comment, if one shoots a bullet into the sky 85 deg from the horizontal at 3,000'/sec and 250,000 RPMs the bullet will land again on the earth not too far from where it was fired but at a velocity of about -350'/sec and maybe 150,000 RPM and, of course, will hit heel first and not point first.

I would think that the rotation (stability) would cause it to land point first. (it flight path would be an arc) But in going thru arc yaw/change in direction of flight would cause lot of drag. I would also think the velocity falling would be a whole lot lower and would be gravity/drag. A projectile fired vertical is not going to return at near muzzle velocity (unless in vacum) because of drag.
If bullet could be fire perfectly vertical ?? it would land heel first as long as it had some rotation? JMO

quote:

I would think that the rotation (stability) would cause it to land point first. (it flight path would be an arc) But in going thru arc yaw/change in direction of flight would cause lot of drag. I would also think the velocity falling would be a whole lot lower and would be gravity/drag. A projectile fired vertical is not going to return at near muzzle velocity (unless in vacum) because of drag.
If bullet could be fire perfectly vertical ?? it would land heel first as long as it had some rotation? JMO

I assumed that the bullet would land at terminal velocity which is around 120 miles per hour...or about 200'/sec but the bullet is a bit more streamlined and I assumed it would fall a bit faster.

As to falling heel first it is my assumption that gyroscopic forces would keep the bullat at 85 Deg to the horizontal at all times.

funny you should bring this up...
Myth Busters had a segment on this not too long ago and they detirmained that a 9mm pistol bullet fired vertically would return to earth in a stable side ways fall at approximatly 130 mph. They then tested this in the desert and it was true.
They did not test what would happen if the trajectory were not plumb vertical. But the generally accepted theory, backed by years of military application, is that the bullet will make the turn at the top and return piont first, gyroscipicly stable. The question remains, at what firing angle is this still valid?
MB also attemped this test with an M1 Garand, but were unable to locate any fallen bullets.

quote:

The question remains, at what firing angle is this still valid?

I can only guess and it would be my guess that at about 60 deg from the horizontal the air friction against the side of the bullet would actually cause it to turn and fall point first. This assumes the rotation of the bullet can be overridden.

On the 9MM pistol bullet.....I believe it as the RPM of the bullet is really minor comapred to the rotation of a centerfire rifle bullet going about 1/4 million RPM.

Further the military (may I assume artillery) also has a relatively slow RPM...but not sure.....anyone know the velocity and twist of a 16" shell from the USS Wisconsin?

BTW the reason I chose 85 deg was so that someone wouldn't post that it's be dangerous and hit me on the head and also to prevent this turnaround caused by air forces on the side of the bullet.

Interesting discussion but it don't kill any elk!!!!

quote:

Originally posted by Wink:
Stonecreek, I don't understand your explanation. How can a bullet rotate more times than the imparted rotation produced by the rifling twist? If in the example I used the rifling twist is 1:16, then how can it rotate faster than once every 16 inches? 150 feet is equal to 1,800 inches. In covering that distance it will rotate 1800 divided by 16 equals 112.5 rotations. That assumes that the rotation won't be slowed by any forces at all. But rotating faster than that? You've lost me.

I think that during my period of inattentiveness Vapodog has answered your query. Yes, the bullet keeps spinning at near its initial rotational speed, even though its foward motion has slowed substantially.

Assume for a moment that at some given distance downrange a bullet had lost a bit over 50% of its forward velocity, but only a couple of percent of its rotational speed. In that case it would be rotating about twice in 16" (of forward movement) rather than the once in 16" when it left the muzzle.

quote:

Originally posted by Rusty Marlin:

quote:

Originally posted by Jon A:

quote:

Originally posted by Stonecreek:
As it is, have you ever been able to tell the difference in left-hand vs. right-hand twist by detecting the difference in torque?

Yes.

Not necessarily right vs left but the torque imparted to the gun by forcing the bullet down the rifling is especially noticable in a big-bore, light-weight handgun. A .475 Lin. in a Casull single action tries to twist out of my hand. The torque as quite pronounced. In a heavy handgun in .44mag I don't even notice the torque, but it's obviously still there.

Since a handgun necessarily sits in the hand (or hands) with its mass centered quite a bit above the hand(s) and somewhat out of alignment with the mass of the hand(s), there will always be a tendency for it to recoil both upward and somewhat to one side. This would be true even if it had an unrifled barrel. How much of the "sideways" recoil can be attributed to assymetry and how much can be attributed to rifling torque is difficult to say, but my guess is that the portion that is most noticable is caused by assymetry. It would be interesting to swap for an opposite-handed identical barrel to see what difference was noted.

Projectile-----Calibre (mm) (rpm) range
FH70-L15 -----155 --------13490-16450
4.5in Mk 8 naval shell
-------------112.8 ---------14480-18090
M80-----------7.62--------- 115650-167320
CB10---------5.66-----------239780-334640

Information above blongs to Dr. Derek Bray, DAPS of Cranfield University
I found it on a Power Point presintaion.

notice the RPM rates of the 155 and the 4.5" shells, they are only around 15,000rpm compared to the 7.62's 140,000.
The larger dia. projectiles have a much higher moment of inertia and therefore need fewer rps for stabilization. I think Vapodog already alluded to this.

Dunlap did a book on gunsmithing that has in it everything I ever wondered about. I literally wore the covers off.
If you ever are thinking about building your first rifle be sure to do a long read of his tome.

I don't remember what it is called (pre something) but there is a 3rd reaction when gyro is turned that would also make it vere of course. Direction of vere depends on rotation. So the arc flight would probably ver left or right from line of flight also. I think this was about the time SuzyQ got up in class to get a drink of water and the rest is history. LOL I don't know where we are going but it's been fun following!

precession?
peter.

quote:

Originally posted by Peter:
precession?
peter.

Yes

quote:

I don't remember what it is called (pre something) but there is a 3rd reaction when gyro is turned that would also make it vere of course.

Maybe someone can explain this....I can find no forces to cause this to happen. Rotation has no component in left right or any direction. What am I missing here.

I've heard people say that a bullet will drift right or left depending on whether the twist is LH or RH.....I'm not so sure but it comes from folks of credibility so I ask myself.....what am I missing here???

vapodog:

I vaguely remember during the Field Artillery Officer Basic Course,that (at least in the dark ages) artillery shells drift to the right, based on their clockwise (viewed from the cannon) rotation. When I asked "why"...the instructors replied with something like: "what's 'why' got to do with anything, it just does..now sit down and shut up". I always assumed that there is more air pressure on the botton portion of the projectile, becasue it's always falling. So the clockwise rotation would cause it to "crawl" to the right. But I must admit, I have never tested or proven my hypothesis.

quote:

So the clockwise rotation would cause it to "crawl" to the tight. But I must admit, I have never tested or proven my hypothesis.

Thank you sir.....you're the first person that has ever suggested that as a force.....and yes, it makes sense...Thank you.

Vapodog,
This might help explain precession but we will have to study it to see if it has any effect on what we are discussing. Have a safe happy Independence Day!
James

http://en.wikipedia.org/wiki/Precession

.

quote:

or is my reasoning in error here ?

It seems that your reasoning is dead on...agreed...

quote:

Originally posted by olarmy:
...I always assumed that there is more air pressure on the botton portion of the projectile, becasue it's always falling. ...

Actually, I believe you will find it is because of the Angle of Incidence.
---

If anyone cares to see it for themselves, you could go to the field and shoot a few cartridges at l-o-n-g distance. There you will notice the effect, because you have to add "Left Clicks" to remain on Target(with a right-hand twist). The wind does not always come from your left.

Or, you can cant the scope slightly to compensate, but this can be trickier (in adjustment) than just doing it correctly to start with.
---

When you see folks talk about l-o-n-g distance shooting and they start mentioning "Clicks of Elevation", if they do not also mention "Clicks of Windage", you can make a relatively safe bet they have never fired a shot at distance.