Does a bullet fired with a clockwise spin travel faster or slower

  • #1
rasanders22
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or the same speed than if it had a counter-clockwise spin?
 

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  • #2
JaredJames
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Why do you believe there'd be a difference?

Perhaps I'd even extend the question: would a spinning bullet travel faster than a non-spinning one?
 
  • #3
Delta2
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It can travel faster slower or at same speed with a non spining bullet.

However if we have two bullets of same speed, one spinning and one non spinning, then the spinning one carries more energy and thus can have more devastating impact on collision with other bodies. Simply put, a spinning bullet behaves not only as a fast moving body but also like a drill.
 
  • #4
vanesch
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It can travel faster slower or at same speed with a non spining bullet.

However if we have two bullets of same speed, one spinning and one non spinning, then the spinning one carries more energy and thus can have more devastating impact on collision with other bodies. Simply put, a spinning bullet behaves not only as a fast moving body but also like a drill.

On the other hand, purely theoretically, if a same amount of energy is transferred to a bullet by the gun, then a spinning bullet must travel slower than a non-spinning bullet, exactly because of the fact that in the last case, the total energy budget has to be divided between the rotational energy and the translational energy.
 
  • #5
Wolf5370
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I think the spinning (rifling) is to help the bullet trace as straight a line as possible as it is less affected by differences in mass, surface and temperature across the bullet. It may help it to cut through the air (in particualr perhaps air currents). One would have thought though, that if the bullet did not spin, it would actually go faster for the same explosive force (as energy would be used to push the bullet only and not to make it spin or overcome the extra drag caused by the rifling in the barrel).

The direction of the spin could make a difference given the direction of the asir currents against it I guess, but as these change (probably several time in a single flight) it would not be a reason to reverse the rifling.
 
  • #6
JaredJames
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I think the spinning (rifling) is to help the bullet trace as straight a line as possible as it is less affected by differences in mass, surface and temperature across the bullet. It may help it to cut through the air (in particualr perhaps air currents). One would have thought though, that if the bullet did not spin, it would actually go faster for the same explosive force (as energy would be used to push the bullet only and not to make it spin or overcome the extra drag caused by the rifling in the barrel).

The direction of the spin could make a difference given the direction of the asir currents against it I guess, but as these change (probably several time in a single flight) it would not be a reason to reverse the rifling.

The spin of the bullet causes it to gyroscopically stabilise itself - that is all. As it is uniform in shape effects from variations in conditions make no difference to the bullets path.

Regardless, it doesn't matter what way it spins. The final trajectory would be the same.

It's only in strong winds or over long ranges that wind effects become and issue - rotation of spin still makes no difference.

A faster bullet is useless if you can't hit anything.
 
  • #7
Phrak
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Does a bullet fired with a clockwise spin travel faster or slower...
...or the same speed than if it had a counter-clockwise spin?

The same. Why?
 
  • #9
sophiecentaur
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The same. Why?

I think it's up to you to suggest "why not?", perhaps.

Isn't the point of the rifling, to give better range? Surely a tumbling bullet would be less aerodynamic and slow down quicker. A ball, of the same mass would be wider and experience more drag than a bullet shaped projectile so a spinning bullet is the best buy.
I wonder whether the gas seal whilst in the barrel is better, too.
 
  • #10
JaredJames
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I think it's up to you to suggest "why not?", perhaps.

I was always under the impression that if you make a claim, it was your responsibility to back it up. As per my initial question, I'm curious why the OP believes it would be slower in one direction than the other.
Isn't the point of the rifling, to give better range? Surely a tumbling bullet would be less aerodynamic and slow down quicker. A ball, of the same mass would be wider and experience more drag than a bullet shaped projectile so a spinning bullet is the best buy.
I wonder whether the gas seal whilst in the barrel is better, too.

Rifling makes the round more accurate and improves the range by stabilising it. Not much more to it. The trade off between a ball and bullet is that a balls profile will give more stopping power, but you lose accuracy and range using them.

I shot an air rifle without rifling once, I'd have been lucky to hit the end of my finger if I'd put it over the end of the barrel.
 
  • #11
sophiecentaur
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Yes - point taken - Your justification would have been needed after his :-).

Thinking again about the effect of tumbling, the same sort of thing would happen with an unstablised bullet (or ball) as with a cricket ball with spin. Low pressure on one side and high pressure on the other , causing a curved path- and in some random sense from shot to shot.
But clockwise or counter clockwise? Nah - no difference - unless we are considering the rotation of the Earth . . . . . . ..

And your 'naff' air gun could just have been 'naff' in many ways. Far eastern import when that meant cheap and cheerful - not like today.
 
  • #12
JaredJames
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But clockwise or counter clockwise? Nah - no difference - unless we are considering the rotation of the Earth . . . . . . ..

Perhaps the galactic rotation should be invoked... :wink:
And your 'naff' air gun could just have been 'naff' in many ways. Far eastern import when that meant cheap and cheerful - not like today.

I'm 21, it was brand new top of the line a few years back and anything but "naff" (not a far eastern import for one). The phrase "not like today" doesn't apply to me. I had two, one was a single shot rifle (rifled) and the other was a semi-automatic. The single shot could hit the target perfectly everytime, but the semi-automatic - due to the law surrounding it - wasn't allow to be rifled, and when you shot it you couldn't hit bugger all. When the C02 cartridge ran down you could actually watch the pellets veering off.
 
  • #13
Ranger Mike
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jarednjames


The trade off between a ball and bullet is that a balls profile will give more stopping power, but you lose accuracy and range using them.

Is not the modern profile of a bullet vastly more aerodynamic than a round ball?
would not the bullet have more speed due to less aero drag than the ball and thus have more impact ( is both weighed the same). Or am i a victim of out dated thinking?
 
  • #14
sophiecentaur
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Perhaps the galactic rotation should be invoked... :wink:


I'm 21, it was brand new top of the line a few years back and anything but "naff" (not a far eastern import for one). The phrase "not like today" doesn't apply to me. I had two, one was a single shot rifle (rifled) and the other was a semi-automatic. The single shot could hit the target perfectly everytime, but the semi-automatic - due to the law surrounding it - wasn't allow to be rifled, and when you shot it you couldn't hit bugger all. When the C02 cartridge ran down you could actually watch the pellets veering off.

That was no air gun - it was a popgun, my boy!!!:wink:

The 'far eastern imports' could well be the best nowadays. "Made in England" used to mean that someone took hours getting a gun 'right' and you paid for it. I think the dreaded Health and Safety thing has spoiled a lot of things.
Shame about the BB gun coming along.
 
  • #15
JaredJames
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Is not the modern profile of a bullet vastly more aerodynamic than a round ball?
would not the bullet have more speed due to less aero drag than the ball and thus have more impact ( is both weighed the same). Or am i a victim of out dated thinking?

Think 9mm round, .45 and .50 caliber. The bigger the round, the greater the stopping power. A small high speed round may have the same momentum as a large slow round, but one of them will do more to 'stop' you than the other.

Imagine I have a 1kg needle with a 1mm diameter and I stab you with it. Yes it may do some damage, but it wouldn't incapacitate you straight away - you could keep coming at me for example. Now imagine I have a 1kg bag of sugar and throw it at you. This has a far greater ability to stop you in your tracks.

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

I'll be honest, I was thinking of a musket ball (around 15mm diameter) against 9mm round when doing the comparison.
 
  • #16
JaredJames
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That was no air gun - it was a popgun, my boy!!!:wink:

It fired a .22 pellet 100 yards and (when on target) could drop a hare in one shot. That's one hell of a "popgun".

Besides, under the definition of airgun, it's well covered.

BB guns are rubbish. Used to have loads of them when I was a kid - best ones from Spain.
 
  • #17
sophiecentaur
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Different circumstances call for either maximum momentum or maximum energy. Sometimes a shotgun is what you need.
 
  • #18
sophiecentaur
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It fired a .22 pellet 100 yards and (when on target) could drop a hare in one shot. That's one hell of a "popgun".

Sounds quite pokey but totally spoiled by the regulations.
If I don't sign off now, I'll never get my shopping done!!!
 
  • #19
JaredJames
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Different circumstances call for either maximum momentum or maximum energy. Sometimes a shotgun is what you need.

Yes, but people seem to confuse the ability of a small bullet going faster with it's ability to "stop" someone. One of the reasons for hollow point 9mm ammo is to give greater stopping power to the weapon.
 
  • #20
JaredJames
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Sounds quite pokey but totally spoiled by the regulations.

100 yards is damn good even for the best air rifles. Granted you could barely hit the floor at that range, but still it's 100 yards.

I only got rid of it because it was so crap with aim.
 
  • #21
rasanders22
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Well the reason I asked was I was thinking of the bullet spinning like a gyroscope and the inertia caused by a left or right spin would cause it to speed up or slow down. LIke how a spinning gyroscope can cause motion in a direction.

As far as weight of a bullet and size. Ive been into shooting for years and reload my own ammo. Personally, I prefer small rounds going very fast out of my ar-15. Not only do I get to hold more rounds (30), but they the 5.56 round creates a very large primary and secondary wound cavity. When the bullet enters your body it begins to rotate. Somewhere around 90 degrees the stress of bullet traving sideways in your body causes it to come apart and explode, showering your organs with bits of metal, not to mention the trauma caused by the pressure wave it crates inside you. Not only that, but the light 5.56 round sheds velocity quicker than heavier handgun rounds, so the risk of shooting my neighbors if I miss someone goes down.
 
  • #22
Phrak
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I think it's up to you to suggest "why not?", perhaps.

Isn't the point of the rifling, to give better range? Surely a tumbling bullet would be less aerodynamic and slow down quicker. A ball, of the same mass would be wider and experience more drag than a bullet shaped projectile so a spinning bullet is the best buy.
I wonder whether the gas seal whilst in the barrel is better, too.

The question is about left hand verse right hand riffling. I suppose the answer is that macroscopic mechanics, where Newton's equations are applicable, the laws of physics are invariant under parity change, and also that the conditions normally encountered shooting a riffle the constituent matter has no strong parity preference of comparable magnitude.

--Actually, come to think about it, we are generally right handed, so the "constituent matter" does have a parity preference. Does a riffled barrel tend to twist a little when fired?
 
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  • #23
Tyrannical
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I'm disappointed there was no "in Australia" clause :tongue2:

The direction of the spin doesn't matter.

Now a spinning bullet will travel faster, farther, more accurate, and with more energy when it strikes the target than a non-spinning bullet. Spinning makes the bullet travel in a straighter path, but it also causes the bullet to meet less air resistance when traveling.
 
  • #24
JaredJames
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but it also causes the bullet to meet less air resistance when traveling.

OK, this has been bothering me for a while and I must ask - why does it encounter less air resistance?
 
  • #25
Tyrannical
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OK, this has been bothering me for a while and I must ask - why does it encounter less air resistance?

The short answer is it is aerodynamic :wink: If it wasn't spinning, it would be prone to tumbling. Just image throwing a football (US) properly with spin, versus throwing it spinning end over end. The nose of the bullet (or football) sort of pushes the air around it. I suppose the same reason nails are pointy at the end instead of flat, when you pound it into wood the wood splits at the point of the nail.

The much longer answer.......

http://waterocket.explorer.free.fr/aerodynamics.htm" [Broken]
 
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  • #26
JaredJames
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The short answer is it is aerodynamic :wink: If it wasn't spinning, it would be prone to tumbling. Just image throwing a football (US) properly with spin, versus throwing it spinning end over end. The nose of the bullet (or football) sort of pushes the air around it.

I understand the whole tumbling thing, but it's the gyroscopic forces that prevent this. The way I see it, the air resistance encountered is the same but the spin means it doesn't affect the bullet in the same way.
I suppose the same reason nails are pointy at the end instead of flat, when you pound it into wood the wood splits at the point of the nail.

Not quite the same thing. Besides the fact that nails don't spin, bullets are the same shape, spinning or not. Yes a flat bullet would encounter the same issues as a flat nail, but that's not the issue.
The much longer answer.......

http://waterocket.explorer.free.fr/aerodynamics.htm" [Broken]

Yeah, I've spent the last three years doing a degree in Aerospace Engineering. Hence my question. I can't see how the spin reduces air resistance - I can only see how it can reduce its effects.
 
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  • #27
Tyrannical
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It's not the spinning, it's that the spinning keeps the bullet straight and hence more aerodynamic. If it didn't spin it would tumble instead of fly straight.
 
  • #28
JaredJames
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It's not the spinning, it's that the spinning keeps the bullet straight and hence more aerodynamic. If it didn't spin it would tumble instead of fly straight.

I fully understand that, but that doesn't mean it reduces air resistance.

The air resistance a spinning bullet undergoes is equal to that of a non-spinning bullet. It's not until the bullet is tumbling that this changes. So the gyroscopic forces prevent the tumbling occurring.

However, the air resistance each encounters up to that point is identical. It's only that one reacts and the other is able to resist.

I'm not seeing it as reducing air resistance, more that it has an increased ability to withstand it.
 
  • #29
sophiecentaur
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I fully understand that, but that doesn't mean it reduces air resistance.

The air resistance a spinning bullet undergoes is equal to that of a non-spinning bullet. It's not until the bullet is tumbling that this changes. So the gyroscopic forces prevent the tumbling occurring.

However, the air resistance each encounters up to that point is identical. It's only that one reacts and the other is able to resist.

I'm not seeing it as reducing air resistance, more that it has an increased ability to withstand it.

As soon as a non spinning bullet emerges, it will tend to yaw / pitch and that will introduce more drag. I can't imagine that tumbling can take very long to occur. SO, albeit as a consequence of not spinning, the drag will end up much higher so the range will suffer - as well as producing the Magnus effect.

I don't understand your last sentence. You don't "withstand" air resistance (except by using an engine), all you can do is to reduce it by a suitable orientation in flight.
 
  • #30
JaredJames
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As soon as a non spinning bullet emerges, it will tend to yaw / pitch and that will introduce more drag. I can't imagine that tumbling can take very long to occur. SO, albeit as a consequence of not spinning, the drag will end up much higher so the range will suffer - as well as producing the Magnus effect.

But a spinning bullet has the magnus effect.
I don't understand your last sentence. You don't "withstand" air resistance (except by using an engine), all you can do is to reduce it by a suitable orientation in flight.

To withstand is to resist. The gyroscopic forces allow the bullet to resist the effects of air resistance better than a non-spinning one.

Once again, I fully understand the tumbling issue. Perhaps I need to word this better:

Imagine two objects moving through the air - let's use two identical rockets (assume stabilising fins). One is spinning rapidly, the other isn't. Does one experience less air resistance than the other?
 
  • #31
sophiecentaur
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A big NO on that one and, of course I agree on that with you that, spinning, per se, is not likely to affect air resistance (although the surface speed of the bullet would be a bit higher; I don't know what effect this could have on the drag as it could increase the volume of turbulent air around the bullet, perhaps.)
I am just pointing our that the consequence of not spinning is that tumbling will occur. Spinning will "resist" the tumbling but I don't see that as "resisting air resistance".
 
  • #32
likephysics
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Can someone explain how spinning would give the bullet Gyroscopic force?
Even spacecraft's spin to maintain course. The reason for both the bullet and spacecraft might be same.
I don't understand how spinning would give it "force".
 
  • #33
kjohnson
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Yes, but people seem to confuse the ability of a small bullet going faster with it's ability to "stop" someone. One of the reasons for hollow point 9mm ammo is to give greater stopping power to the weapon.

Obviously there is some debate between energy and stopping power possessed by a bullet. Now I am no expert on firearms or ammunition, but here is my take:

A smaller bullet my be able to be fired with a greater velocity thus increasing its kinetic energy greatly since KE=(1/2)mv^2. But if a small bullet encounters less resistance while traveling through the target then it will leave the target with some velocity left. So the energy transferred to the target is equal to the difference in kinetic energy of bullet (neglecting heat, etc.).

Now a larger bullet may carry less initial kinetic energy, but experience enough resistance to stop somewhere in the target (or at least come out with a much lower velocity). Because of this the change in KE and thus energy transferred will be greater.

Of course this is not taking into effect the tumbling of the bullet within the target. If a small fast bullet tumbles withing the target then its velocity will greatly slowed or stopped causing much greater stopping power. I've heard of those little 22 caliber bullets people like to make fun of doing a lot of damage because of this. They enter the target tumble around and don't exit. So in a pure physical sense stopping power is only related to the amount of energy transfer. Taking into account what vitals are hit and bleed out times is an entire different story. This is only talking about the stopping force felt.
 
  • #34
turbo
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Direction of twist is at the whim of the manufacturer. Harry Pope built some of the finest target barrels ever, and his preference was for left hand twist. The direction of twist was not the source of the accuracy, though. His rifling featured wide shallow grooves and narrow lands that minimized friction while retaining control. Plus he fitted "false muzzles" to the ends of his target barrels to facilitate muzzle loading of the bullets separately from the cartridges. Muzzle-loading soft lead bullets prevented the burrs and lack of uniformity on the base that resulted from breech-loading.

He also used "gain twist" rifling in which the rifling near the breech twisted more slowly than the rifling near the muzzle. He claimed that having a shallower twist near the breech allowed the bullet to accelerate faster initially, and the steeper twist at the muzzle imparted an accelerated spin to the bullet for gyroscopic stability. Given the impressive target scores racked up by users of his barrels, it seems that he knew exactly what he was talking about.
 
  • #35
sophiecentaur
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What is "gyroscopic force"? Do they mean gyroscopic moment? Spin will tend to keep the bullet orientated along the direction of the spin axis. It will precess a little but not significantly before it has hit its target.
Google Gyroscope and Angular Momentum for more info and some animations / explanations.
 

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