Helping a new shooter that is interested in Long Range Precision shooting. Talking about bullets of different weights, some needing a little time or room to settle down and show their potential (at distance). His line of thinking is that if it's shooting .75 MOA at 100, then it will have to shoot .75 MOA all the way out to it's range limits ie it isn't possible to shoot "better" as the range increases. He understands that the group isn't "shrinking". Can you guys explain if a bullet actually lays down/settles in, call it what ever you want, after it passes through from 100 to 300 yards for example? I've "heard" this the case with .338's in close for example. I don't want to feed him bs, and I don't have the ballistic background to KNOW that is a fact or just a theory. Thanks.
Range Report Bullet "Settling/Laying Down" - Fact or Theory?
- Thread starter tnichols
- Start date
Re: Bullet "Settling/Laying Down" - Fact or Theory?
Sometimes bullets that are being slightly under spun at the muzzle will "fall asleep" downrange as they gain stability. This happens because the rotation of the bullet is fairly constant throughout it's flight while the forces working to make it unstable decrease with the velocity decreasing("Rigidity of the spinning mass" Divided by the "Overturning aerodynamic torque"). This only happens with bullets that leave the barrel with marginal stability however. If your barrel has adequate twist for the length of bullet being used it should be stable at the muzzle.
The weight of a bullet is less important than it's length in terms of how much spin it needs for proper stability. For instance you may not have any trouble stabilizing a 7mm 175gr SMK while a 7mm 175gr Berger might be very unstable out of the same barrel because the Berger bullet is much longer and requires faster rotation for stability.
Sometimes bullets that are being slightly under spun at the muzzle will "fall asleep" downrange as they gain stability. This happens because the rotation of the bullet is fairly constant throughout it's flight while the forces working to make it unstable decrease with the velocity decreasing("Rigidity of the spinning mass" Divided by the "Overturning aerodynamic torque"). This only happens with bullets that leave the barrel with marginal stability however. If your barrel has adequate twist for the length of bullet being used it should be stable at the muzzle.
The weight of a bullet is less important than it's length in terms of how much spin it needs for proper stability. For instance you may not have any trouble stabilizing a 7mm 175gr SMK while a 7mm 175gr Berger might be very unstable out of the same barrel because the Berger bullet is much longer and requires faster rotation for stability.
Re: Bullet "Settling/Laying Down" - Fact or Theory?
New shooter here. I understand that the bullet can leave the barrel with a bit of a wiggle, and can stabilize during flight due to combination of rotation and aerodynamic shape. Just not buyin the notion that since the bullet is more stable further downrange, a .75 moa group at 100 yards would be smaller if it had been allowed to travel to 300. Rare occasion: A puff of wind might push a 'would be flyer' back into the group.
New shooter here. I understand that the bullet can leave the barrel with a bit of a wiggle, and can stabilize during flight due to combination of rotation and aerodynamic shape. Just not buyin the notion that since the bullet is more stable further downrange, a .75 moa group at 100 yards would be smaller if it had been allowed to travel to 300. Rare occasion: A puff of wind might push a 'would be flyer' back into the group.
Re: Bullet "Settling/Laying Down" - Fact or Theory?
The smartest ballisticians I know concede this does happen. I have seen it three times over 34 years of competitive shooting but nobody can really explain it or even more important, repeat it at will. It just happens.
Is there in bore yaw? yes
Are there bullets that may not be concentric and not balanced ? yes
Can a poorly cut crown affect post bore yaw? yes
Add all that up and nobody really knows why it happens.
The smartest ballisticians I know concede this does happen. I have seen it three times over 34 years of competitive shooting but nobody can really explain it or even more important, repeat it at will. It just happens.
Is there in bore yaw? yes
Are there bullets that may not be concentric and not balanced ? yes
Can a poorly cut crown affect post bore yaw? yes
Add all that up and nobody really knows why it happens.
Re: Bullet "Settling/Laying Down" - Fact or Theory?
Some thoughts/research on the subject:
http://appliedballisticsllc.com/epswerve.html
Note the video can be misleading if you don't read the article. Also be careful not to get hypnotized!
-Bryan
Some thoughts/research on the subject:
http://appliedballisticsllc.com/epswerve.html
Note the video can be misleading if you don't read the article. Also be careful not to get hypnotized!
-Bryan
Re: Bullet "Settling/Laying Down" - Fact or Theory?
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: ArmchairElite</div><div class="ubbcode-body">Sometimes bullets that are being slightly <span style="font-weight: bold"><span style="color: #FF0000">Over</span></span> spun at the muzzle will "fall asleep" downrange as they <span style="color: #FF0000">Loose Overstabilization</span>. This happens because the rotation of the bullet is fairly constant throughout it's flight while the forces working to make it unstable decrease with the velocity decreasing("Rigidity of the spinning mass" Divided by the "Overturning aerodynamic torque").
This only happens with bullets that leave the barrel with marginal stability however. If your barrel has adequate twist for the length of bullet being used it should be stable at the muzzle.
<span style="color: #FF0000"> If the bullet is stabilized, It is stabilized.
"Marginally Stabilized" is a term used to take into consideration variables like differences in bullet length, Velocity, Temperature, Altitude and Air pressure.
A Bullet that is not stabilized will act like a knuckle ball. It cannot become more stabilized. It can only become even less stabilized.</span>
The weight of a bullet is less important than it's length in terms of how much spin it needs for proper stability. For instance you may not have any trouble stabilizing a 7mm 175gr SMK while a 7mm 175gr Berger might be very unstable out of the same barrel because the Berger bullet is much longer and requires faster rotation for stability. </div></div>
Fixed it
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: ArmchairElite</div><div class="ubbcode-body">Sometimes bullets that are being slightly <span style="font-weight: bold"><span style="color: #FF0000">Over</span></span> spun at the muzzle will "fall asleep" downrange as they <span style="color: #FF0000">Loose Overstabilization</span>. This happens because the rotation of the bullet is fairly constant throughout it's flight while the forces working to make it unstable decrease with the velocity decreasing("Rigidity of the spinning mass" Divided by the "Overturning aerodynamic torque").
This only happens with bullets that leave the barrel with marginal stability however. If your barrel has adequate twist for the length of bullet being used it should be stable at the muzzle.
<span style="color: #FF0000"> If the bullet is stabilized, It is stabilized.
"Marginally Stabilized" is a term used to take into consideration variables like differences in bullet length, Velocity, Temperature, Altitude and Air pressure.
A Bullet that is not stabilized will act like a knuckle ball. It cannot become more stabilized. It can only become even less stabilized.</span>
The weight of a bullet is less important than it's length in terms of how much spin it needs for proper stability. For instance you may not have any trouble stabilizing a 7mm 175gr SMK while a 7mm 175gr Berger might be very unstable out of the same barrel because the Berger bullet is much longer and requires faster rotation for stability. </div></div>
Fixed it
Re: Bullet "Settling/Laying Down" - Fact or Theory?
I certainly belive that bullets can/will engrave the rifling with poor concentricity. Those bullets will wobble their way down the bore, and probably wobble for a while on their way down range, too. Hell, maybe they'll wobble all the way downrange. These bullets will show poor consistency, and will not print a precise group.
I also believe a poor crown can induce some yaw or wobble, which will also hurt precision.
However, I don't believe that in still air:
1) A bullet traveling along a path that does *not* lead to "the group" is going to suddently make an educated decision to veer off it's current path, and onto the correct path.
2) A bullet traveling along the correct path to "the group" is going to suddenly decide to make a random turn off that path.
I certainly belive that bullets can/will engrave the rifling with poor concentricity. Those bullets will wobble their way down the bore, and probably wobble for a while on their way down range, too. Hell, maybe they'll wobble all the way downrange. These bullets will show poor consistency, and will not print a precise group.
I also believe a poor crown can induce some yaw or wobble, which will also hurt precision.
However, I don't believe that in still air:
1) A bullet traveling along a path that does *not* lead to "the group" is going to suddently make an educated decision to veer off it's current path, and onto the correct path.
2) A bullet traveling along the correct path to "the group" is going to suddenly decide to make a random turn off that path.
Re: Bullet "Settling/Laying Down" - Fact or Theory?
Human Element .... we cause some groups to print better at long range vs shorter range. as noted, once off target it stays off and it is either stable or not. Especially at 100 yards... that is a lot of time to stabilize.
Our perception is the determining factor, guys will focus on sound and recoil on targets up close and then actually focus on the reticle & target downrange because they can't see the impacts and will actually shoot better.
Human Element .... we cause some groups to print better at long range vs shorter range. as noted, once off target it stays off and it is either stable or not. Especially at 100 yards... that is a lot of time to stabilize.
Our perception is the determining factor, guys will focus on sound and recoil on targets up close and then actually focus on the reticle & target downrange because they can't see the impacts and will actually shoot better.
Re: Bullet "Settling/Laying Down" - Fact or Theory?
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Brutas</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: ArmchairElite</div><div class="ubbcode-body">Sometimes bullets that are being slightly <span style="font-weight: bold"><span style="color: #FF0000">Over</span></span> spun at the muzzle will "fall asleep" downrange as they <span style="color: #FF0000">Loose Overstabilization</span>. This happens because the rotation of the bullet is fairly constant throughout it's flight while the forces working to make it unstable decrease with the velocity decreasing("Rigidity of the spinning mass" Divided by the "Overturning aerodynamic torque").
This only happens with bullets that leave the barrel with marginal stability however. If your barrel has adequate twist for the length of bullet being used it should be stable at the muzzle.
<span style="color: #FF0000"> If the bullet is stabilized, It is stabilized.
"Marginally Stabilized" is a term used to take into consideration variables like differences in bullet length, Velocity, Temperature, Altitude and Air pressure.
A Bullet that is not stabilized will act like a knuckle ball. It cannot become more stabilized. It can only become even less stabilized.</span>
The weight of a bullet is less important than it's length in terms of how much spin it needs for proper stability. For instance you may not have any trouble stabilizing a 7mm 175gr SMK while a 7mm 175gr Berger might be very unstable out of the same barrel because the Berger bullet is much longer and requires faster rotation for stability. </div></div>
Fixed it </div></div>Please read Chapter 10(pg135) of Bryon Litz book if you want to continue "fixing" these types of things.
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Brutas</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: ArmchairElite</div><div class="ubbcode-body">Sometimes bullets that are being slightly <span style="font-weight: bold"><span style="color: #FF0000">Over</span></span> spun at the muzzle will "fall asleep" downrange as they <span style="color: #FF0000">Loose Overstabilization</span>. This happens because the rotation of the bullet is fairly constant throughout it's flight while the forces working to make it unstable decrease with the velocity decreasing("Rigidity of the spinning mass" Divided by the "Overturning aerodynamic torque").
This only happens with bullets that leave the barrel with marginal stability however. If your barrel has adequate twist for the length of bullet being used it should be stable at the muzzle.
<span style="color: #FF0000"> If the bullet is stabilized, It is stabilized.
"Marginally Stabilized" is a term used to take into consideration variables like differences in bullet length, Velocity, Temperature, Altitude and Air pressure.
A Bullet that is not stabilized will act like a knuckle ball. It cannot become more stabilized. It can only become even less stabilized.</span>
The weight of a bullet is less important than it's length in terms of how much spin it needs for proper stability. For instance you may not have any trouble stabilizing a 7mm 175gr SMK while a 7mm 175gr Berger might be very unstable out of the same barrel because the Berger bullet is much longer and requires faster rotation for stability. </div></div>
Fixed it </div></div>Please read Chapter 10(pg135) of Bryon Litz book if you want to continue "fixing" these types of things.
Re: Bullet "Settling/Laying Down" - Fact or Theory?
Thanks for the responses fella's. Our new shooter was following along with this thread and did register, so I hope he found the answer/info that he was looking for.
By the way, he has been shooting a rifle of mine and is doing EXTREMELY well. He wrung steel late Sunday afternoon for the first time at around 500 yards and I told him that will be the most expensive sound he will ever hear
.
Thanks for the responses fella's. Our new shooter was following along with this thread and did register, so I hope he found the answer/info that he was looking for.
By the way, he has been shooting a rifle of mine and is doing EXTREMELY well. He wrung steel late Sunday afternoon for the first time at around 500 yards and I told him that will be the most expensive sound he will ever hear
Re: Bullet "Settling/Laying Down" - Fact or Theory?
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: RandyG1</div><div class="ubbcode-body">New shooter here. I understand that the bullet can leave the barrel with a bit of a wiggle, and can stabilize during flight due to combination of rotation and aerodynamic shape. Just not buyin the notion that since the bullet is more stable further downrange, a .75 moa group at 100 yards would be smaller if it had been allowed to travel to 300. Rare occasion: A puff of wind might push a 'would be flyer' back into the group. </div></div>
Sounds like the new shooter is a pretty logical thinker to me. Long range rifle is just the thing to drive him crazy, or keep him sane, as the case may be.
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: RandyG1</div><div class="ubbcode-body">New shooter here. I understand that the bullet can leave the barrel with a bit of a wiggle, and can stabilize during flight due to combination of rotation and aerodynamic shape. Just not buyin the notion that since the bullet is more stable further downrange, a .75 moa group at 100 yards would be smaller if it had been allowed to travel to 300. Rare occasion: A puff of wind might push a 'would be flyer' back into the group. </div></div>
Sounds like the new shooter is a pretty logical thinker to me. Long range rifle is just the thing to drive him crazy, or keep him sane, as the case may be.
Re: Bullet "Settling/Laying Down" - Fact or Theory?
BIG Thank You to tnichols for putting this out for all to shoot at and for taking me under his wing...and to all those who took the time to respond and quickly cut to the truth of this issue. Your level of expertise is daunting, and greatly appreciated. Heard it said "Never does a man stand so tall, as when he stoops to help a child". Thank you all
BIG Thank You to tnichols for putting this out for all to shoot at and for taking me under his wing...and to all those who took the time to respond and quickly cut to the truth of this issue. Your level of expertise is daunting, and greatly appreciated. Heard it said "Never does a man stand so tall, as when he stoops to help a child". Thank you all
Re: Bullet "Settling/Laying Down" - Fact or Theory?
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Lowlight</div><div class="ubbcode-body">Human Element .... we cause some groups to print better at long range vs shorter range. as noted, once off target it stays off and it is either stable or not. Especially at 100 yards... that is a lot of time to stabilize.
Our perception is the determining factor, guys will focus on sound and recoil on targets up close and then actually focus on the reticle & target downrange because they can't see the impacts and will actually shoot better.
</div></div>
i see the same effect personally by target size. Range is same thing. if i use 1/2 inch dots i hit them, if i use three inch shoot and see's, i hit them too. all over. Having that smaller target always makes me pay more attention and correct things that i find myself "allowing" on big targets. NPOA being good example. i can have absolutely no npoa and hit a 3 inch sticker so i become lax. If i fk up my npao on half inch dot i miss wildly. I hate missing so mentally i make that leap and do what i should always do. stupid, but true.
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Lowlight</div><div class="ubbcode-body">Human Element .... we cause some groups to print better at long range vs shorter range. as noted, once off target it stays off and it is either stable or not. Especially at 100 yards... that is a lot of time to stabilize.
Our perception is the determining factor, guys will focus on sound and recoil on targets up close and then actually focus on the reticle & target downrange because they can't see the impacts and will actually shoot better.
</div></div>
i see the same effect personally by target size. Range is same thing. if i use 1/2 inch dots i hit them, if i use three inch shoot and see's, i hit them too. all over. Having that smaller target always makes me pay more attention and correct things that i find myself "allowing" on big targets. NPOA being good example. i can have absolutely no npoa and hit a 3 inch sticker so i become lax. If i fk up my npao on half inch dot i miss wildly. I hate missing so mentally i make that leap and do what i should always do. stupid, but true.
Re: Bullet "Settling/Laying Down" - Fact or Theory?
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: turbo54</div><div class="ubbcode-body"> I don't believe that in still air:
1) A bullet traveling along a path that does *not* lead to "the group" is going to suddently make an educated decision to veer off it's current path, and onto the correct path.
2) A bullet traveling along the correct path to "the group" is going to suddenly decide to make a random turn off that path.
</div></div>
of course the bullet does not decide to change course, but the fluid that is traveling in, air, is never truly "still" - except at absolute zero - and has the possibility of pushing the bullet in any direction - the chance of this push "helping" the bullet into the group is almost none
in the case #1 from turbos post there is only a 1 in 4 chance that any influence on bullet travel will result in the impact being closer to the center of the "group" (3 in 4 chance that movement will take the bullet away from center)
in case #2 there is always IMO, a chance for a bullet to be influenced by the air, no matter how calm it feels, but a "push" has 0% chance of helping the group and 100% chance of hurting it
what this adds up to is that as a bullet travels through more air, no matter how calm it feels, the relative group size (in angular measure) must always increase, never staying the same or decreasing
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: turbo54</div><div class="ubbcode-body"> I don't believe that in still air:
1) A bullet traveling along a path that does *not* lead to "the group" is going to suddently make an educated decision to veer off it's current path, and onto the correct path.
2) A bullet traveling along the correct path to "the group" is going to suddenly decide to make a random turn off that path.
</div></div>
of course the bullet does not decide to change course, but the fluid that is traveling in, air, is never truly "still" - except at absolute zero - and has the possibility of pushing the bullet in any direction - the chance of this push "helping" the bullet into the group is almost none
in the case #1 from turbos post there is only a 1 in 4 chance that any influence on bullet travel will result in the impact being closer to the center of the "group" (3 in 4 chance that movement will take the bullet away from center)
in case #2 there is always IMO, a chance for a bullet to be influenced by the air, no matter how calm it feels, but a "push" has 0% chance of helping the group and 100% chance of hurting it
what this adds up to is that as a bullet travels through more air, no matter how calm it feels, the relative group size (in angular measure) must always increase, never staying the same or decreasing
Re: Bullet "Settling/Laying Down" - Fact or Theory?
Actually, the really expensive sounds tend to come out from under a hood...
For me, anyway...
Actually, the really expensive sounds tend to come out from under a hood...
For me, anyway...
Re: Bullet "Settling/Laying Down" - Fact or Theory?
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Graham</div><div class="ubbcode-body">With regard to stability for a given twist-rate, either a bullet is stable, or it isn't. </div></div>"Also understand that there is no hard line between where a bullet will be completely stable, vs out of control. There is quite a large grey area where the bullet has marginal stability, somewhere between an Sg of 1.0 to 1.1. Consider a bullet launched with marginal stability (lower than recommended twist). This bullet will fly with some amount of pitching and yawing until Sg improves enough (thru loss of velocity) to restore point-forward flight. This phenomenon is often described as the bullet going to sleep (if twist is too slow, the bullet will simply tumble instead of going to sleep)."
Bryon Litz
Applied Ballistics For Long-Range Shooting
Pages 138&139
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Graham</div><div class="ubbcode-body">With regard to stability for a given twist-rate, either a bullet is stable, or it isn't. </div></div>"Also understand that there is no hard line between where a bullet will be completely stable, vs out of control. There is quite a large grey area where the bullet has marginal stability, somewhere between an Sg of 1.0 to 1.1. Consider a bullet launched with marginal stability (lower than recommended twist). This bullet will fly with some amount of pitching and yawing until Sg improves enough (thru loss of velocity) to restore point-forward flight. This phenomenon is often described as the bullet going to sleep (if twist is too slow, the bullet will simply tumble instead of going to sleep)."
Bryon Litz
Applied Ballistics For Long-Range Shooting
Pages 138&139
Re: Bullet "Settling/Laying Down" - Fact or Theory?
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: ArmchairElite</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Graham</div><div class="ubbcode-body">With regard to stability for a given twist-rate, either a bullet is stable, or it isn't. </div></div>"Also understand that there is no hard line between where a bullet will be completely stable, vs out of control. There is quite a large grey area where the bullet has marginal stability, somewhere between an Sg of 1.0 to 1.1. Consider a bullet launched with marginal stability (lower than recommended twist). This bullet will fly with some amount of pitching and yawing until Sg improves enough (thru loss of velocity) to restore point-forward flight. This phenomenon is often described as the bullet going to sleep (if twist is too slow, the bullet will simply tumble instead of going to sleep)."
Bryon Litz
Applied Ballistics For Long-Range Shooting
Pages 138&139 </div></div>
However I dont think this really applies to this.... Most peoples bullets are stable( over 1.4), so it is not the phenomenon you are describing.
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: ArmchairElite</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Graham</div><div class="ubbcode-body">With regard to stability for a given twist-rate, either a bullet is stable, or it isn't. </div></div>"Also understand that there is no hard line between where a bullet will be completely stable, vs out of control. There is quite a large grey area where the bullet has marginal stability, somewhere between an Sg of 1.0 to 1.1. Consider a bullet launched with marginal stability (lower than recommended twist). This bullet will fly with some amount of pitching and yawing until Sg improves enough (thru loss of velocity) to restore point-forward flight. This phenomenon is often described as the bullet going to sleep (if twist is too slow, the bullet will simply tumble instead of going to sleep)."
Bryon Litz
Applied Ballistics For Long-Range Shooting
Pages 138&139 </div></div>
However I dont think this really applies to this.... Most peoples bullets are stable( over 1.4), so it is not the phenomenon you are describing.
Re: Bullet "Settling/Laying Down" - Fact or Theory?
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: ArmchairElite</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Graham</div><div class="ubbcode-body">With regard to stability for a given twist-rate, either a bullet is stable, or it isn't. </div></div>"Also understand that there is no hard line between where a bullet will be completely stable, vs out of control. There is quite a large grey area where the bullet has marginal stability, somewhere between an Sg of 1.0 to 1.1. Consider a bullet launched with marginal stability (lower than recommended twist). This bullet will fly with some amount of pitching and yawing until Sg improves enough (thru loss of velocity) to restore point-forward flight. This phenomenon is often described as the bullet going to sleep (if twist is too slow, the bullet will simply tumble instead of going to sleep)."
Bryon Litz
Applied Ballistics For Long-Range Shooting Pages 138&139 </div></div>Thank you for proving my point.
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: ArmchairElite</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Graham</div><div class="ubbcode-body">With regard to stability for a given twist-rate, either a bullet is stable, or it isn't. </div></div>"Also understand that there is no hard line between where a bullet will be completely stable, vs out of control. There is quite a large grey area where the bullet has marginal stability, somewhere between an Sg of 1.0 to 1.1. Consider a bullet launched with marginal stability (lower than recommended twist). This bullet will fly with some amount of pitching and yawing until Sg improves enough (thru loss of velocity) to restore point-forward flight. This phenomenon is often described as the bullet going to sleep (if twist is too slow, the bullet will simply tumble instead of going to sleep)."
Bryon Litz
Applied Ballistics For Long-Range Shooting Pages 138&139 </div></div>Thank you for proving my point.
Re: Bullet "Settling/Laying Down" - Fact or Theory?
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Graham</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: ArmchairElite</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Graham</div><div class="ubbcode-body">With regard to stability for a given twist-rate, either a bullet is stable, or it isn't. </div></div>"Also understand that there is no hard line between where a bullet will be completely stable, vs out of control. There is quite a large grey area where the bullet has marginal stability, somewhere between an Sg of 1.0 to 1.1. Consider a bullet launched with marginal stability (lower than recommended twist). This bullet will fly with some amount of pitching and yawing until Sg improves enough (thru loss of velocity) to restore point-forward flight. This phenomenon is often described as the bullet going to sleep (if twist is too slow, the bullet will simply tumble instead of going to sleep)."
Bryon Litz
Applied Ballistics For Long-Range Shooting Pages 138&139 </div></div>Thank you for proving my point. </div></div>If I proved your point then the point you were making was the opposite of what you were saying. I'm glad I could help none the less
.
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Graham</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: ArmchairElite</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Graham</div><div class="ubbcode-body">With regard to stability for a given twist-rate, either a bullet is stable, or it isn't. </div></div>"Also understand that there is no hard line between where a bullet will be completely stable, vs out of control. There is quite a large grey area where the bullet has marginal stability, somewhere between an Sg of 1.0 to 1.1. Consider a bullet launched with marginal stability (lower than recommended twist). This bullet will fly with some amount of pitching and yawing until Sg improves enough (thru loss of velocity) to restore point-forward flight. This phenomenon is often described as the bullet going to sleep (if twist is too slow, the bullet will simply tumble instead of going to sleep)."
Bryon Litz
Applied Ballistics For Long-Range Shooting Pages 138&139 </div></div>Thank you for proving my point. </div></div>If I proved your point then the point you were making was the opposite of what you were saying. I'm glad I could help none the less
Re: Bullet "Settling/Laying Down" - Fact or Theory?
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: ArmchairElite</div><div class="ubbcode-body">If I proved your point then the point you were making was the opposite of what you were saying. I'm glad I could help none the less . </div></div>The key to good criticism is reading comprehension. And the key to good argument is to stay on point.
I do, of course, defer to Bryan, as he is - almost literally - next door to me. But in that passage he is talking about a bullet spun marginally which then slows down. It does not change the accuracy of what I posted.
The longer a bullet is to be in flight the more initial rotation (barrel twist) it needs to keep spinning about its rotational center. Of course the farther the bullet flies, and the slower it gets, the less stable it becomes. Therefore a mathematically ideal twist rate can be, or become, too slow under certain conditions.
But the fact that there is no hard line at which a bullet becomes <span style="font-style: italic">completely</span> stable simply reinforces the fact that either a bullet is stable, and perhaps it 'settles down' and stops yawing when velocity decreases, or the bullet is not stable and it tumbles.
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: ArmchairElite</div><div class="ubbcode-body">If I proved your point then the point you were making was the opposite of what you were saying. I'm glad I could help none the less
I do, of course, defer to Bryan, as he is - almost literally - next door to me. But in that passage he is talking about a bullet spun marginally which then slows down. It does not change the accuracy of what I posted.
The longer a bullet is to be in flight the more initial rotation (barrel twist) it needs to keep spinning about its rotational center. Of course the farther the bullet flies, and the slower it gets, the less stable it becomes. Therefore a mathematically ideal twist rate can be, or become, too slow under certain conditions.
But the fact that there is no hard line at which a bullet becomes <span style="font-style: italic">completely</span> stable simply reinforces the fact that either a bullet is stable, and perhaps it 'settles down' and stops yawing when velocity decreases, or the bullet is not stable and it tumbles.
Re: Bullet "Settling/Laying Down" - Fact or Theory?
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Graham</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: ArmchairElite</div><div class="ubbcode-body">If I proved your point then the point you were making was the opposite of what you were saying. I'm glad I could help none the less . </div></div>The key to good criticism is reading comprehension. And the key to good argument is to stay on point.
The longer a bullet is to be in flight the more initial rotation (barrel twist) it needs to keep spinning about its rotational center. Of course the farther the bullet flies, and the slower it gets, the less stable it becomes. Therefore a mathematically ideal twist rate can be, or become, too slow under certain conditions.</div></div>"Velocity also comes into play as the bullet flies downrange, its forward velocity declines much faster than its losing rotational velocity. This means that the aerodynamic overturning torque diminishes at a faster rate than the rigidity of the spinning mass, so the gyroscopic stability of the bullet actually increases over its flight. Over a long-range trajectory, a bullet that was launched with an Sg of 1.5 at the muzzle can have its Sg grow to 4.0 or 5.0 or more by the time it reaches the target. In other words, at the muzzle is where Sg will be at a minimum, and it grows as the bullet flies downrange."
Bryan Litz
pages 137&138
I appreciate the conversation tips Graham, but you still have it backwards
. Maybe your neighbor will loan you a copy of his book to read 
.
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Graham</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: ArmchairElite</div><div class="ubbcode-body">If I proved your point then the point you were making was the opposite of what you were saying. I'm glad I could help none the less
The longer a bullet is to be in flight the more initial rotation (barrel twist) it needs to keep spinning about its rotational center. Of course the farther the bullet flies, and the slower it gets, the less stable it becomes. Therefore a mathematically ideal twist rate can be, or become, too slow under certain conditions.</div></div>"Velocity also comes into play as the bullet flies downrange, its forward velocity declines much faster than its losing rotational velocity. This means that the aerodynamic overturning torque diminishes at a faster rate than the rigidity of the spinning mass, so the gyroscopic stability of the bullet actually increases over its flight. Over a long-range trajectory, a bullet that was launched with an Sg of 1.5 at the muzzle can have its Sg grow to 4.0 or 5.0 or more by the time it reaches the target. In other words, at the muzzle is where Sg will be at a minimum, and it grows as the bullet flies downrange."
Bryan Litz
pages 137&138
I appreciate the conversation tips Graham, but you still have it backwards
Re: Bullet "Settling/Laying Down" - Fact or Theory?
He is right Graham, stability increases at range. Put another way, as the bullet loses the majority of its velocity, it is also losing a lot of the aerodynamic force on the nose forward of the center of gravity. This force is constantly try to turn the nose over, but on a stable bullet the gyroscopic forces from the spin prevent it from turning over. The bullet still has the vast majority of that spin even while it has lost most of its velocity. When a bullet tumbles transonic to subsonic, it isn't because of the twist it is more the shape of the bullet.
I do agree with your first post though. The bullet either tumbles, or it flies nose first. One is stable, the other is not.
He is right Graham, stability increases at range. Put another way, as the bullet loses the majority of its velocity, it is also losing a lot of the aerodynamic force on the nose forward of the center of gravity. This force is constantly try to turn the nose over, but on a stable bullet the gyroscopic forces from the spin prevent it from turning over. The bullet still has the vast majority of that spin even while it has lost most of its velocity. When a bullet tumbles transonic to subsonic, it isn't because of the twist it is more the shape of the bullet.
I do agree with your first post though. The bullet either tumbles, or it flies nose first. One is stable, the other is not.
Re: Bullet "Settling/Laying Down" - Fact or Theory?
KY, I know what you are saying about gyroscopic stability - meaning that the velocity decreases faster than RPMs do. I don't dispute that.
But...
Armchair, to borrrow a phrase from Frank: You are mixing apples and oranges. It's good that you are reading Litz's book, but it does nothing for the discussion on this Thread to keep quoting different parts of it verbatim for the simple purpose of repeatedly announcing that I am wrong.
When I say the bullet gets less stable the farther it flies I am saying that the bullet, as it slows down, gets affected more and more by the external forces that are acting upon it. As a practical matter those forces are what we must concern ourselves with when we make our decisions.
Think about the application of what you are saying: Relevant to twist rate, if we made our decision according to the theory you quoted we would all get very slow twist barrels because we shoot very far. If you were correct, we wouldn't care about an initial Sg of 1.0 at the muzzle because we know that by the time the bullet gets to the target is has slowed enough to make the Sg a 1.7.
Of course we know that's not how it works: We need fast-twist barrels, and we use ever faster twists the slower the bullet ends-up... Because either a bullet is stable; or it isn't.
KY, I know what you are saying about gyroscopic stability - meaning that the velocity decreases faster than RPMs do. I don't dispute that.
But...
Armchair, to borrrow a phrase from Frank: You are mixing apples and oranges. It's good that you are reading Litz's book, but it does nothing for the discussion on this Thread to keep quoting different parts of it verbatim for the simple purpose of repeatedly announcing that I am wrong.
When I say the bullet gets less stable the farther it flies I am saying that the bullet, as it slows down, gets affected more and more by the external forces that are acting upon it. As a practical matter those forces are what we must concern ourselves with when we make our decisions.
Think about the application of what you are saying: Relevant to twist rate, if we made our decision according to the theory you quoted we would all get very slow twist barrels because we shoot very far. If you were correct, we wouldn't care about an initial Sg of 1.0 at the muzzle because we know that by the time the bullet gets to the target is has slowed enough to make the Sg a 1.7.
Of course we know that's not how it works: We need fast-twist barrels, and we use ever faster twists the slower the bullet ends-up... Because either a bullet is stable; or it isn't.
Re: Bullet "Settling/Laying Down" - Fact or Theory?
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Graham</div><div class="ubbcode-body">KY, I know what you are saying about gyroscopic stability - meaning that the velocity decreases faster than RPMs do. I don't dispute that.
But...
Armchair, to borrrow a phrase from Frank: You are mixing apples and oranges. It's good that you are reading Litz's book, but it does nothing for the discussion on this Thread to keep quoting different parts of it verbatim for the simple purpose of repeatedly announcing that I am wrong.
When I say the bullet gets less stable the farther it flies I am saying that the bullet, as it slows down, gets affected more and more by the external forces that are acting upon it. As a practical matter those forces are what we must concern ourselves with when we make our decisions.
Think about the application of what you are saying: Relevant to twist rate, if we made our decision according to the theory you quoted we would all get very slow twist barrels because we shoot very far. If you were correct, we wouldn't care about an initial Sg of 1.0 at the muzzle because we know that by the time the bullet gets to the target is has slowed enough to make the Sg a 1.7.
Of course we know that's not how it works: We need fast-twist barrels, and we use ever faster twists the slower the bullet ends-up... Because either a bullet is stable; or it isn't. </div></div>I'm not trying to take shots at you. It just appears to me that when I point something out you put some kind of spin on it and send it back my way. Look, I'm wrong quite a bit. I don't like being wrong but it's part of life and I learn from it and move on. In this case I think that some of the things you said were not correct and we could debate them indefinitely if we are both more interested in winning an argument than clarifying the truth. I've seen many of your posts and I'm well aware that you are a very intelligent person, but I still disagree. It's nothing personal.
I've already said what I intended to say so I don't feel the need to get into semantics. These discussions are supposed to be geared towards mutual instruction, learning and sharing of information. If you feel that I was simply attacking you instead of contributing to the conversation then I apologize. It was not my intention.
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Graham</div><div class="ubbcode-body">KY, I know what you are saying about gyroscopic stability - meaning that the velocity decreases faster than RPMs do. I don't dispute that.
But...
Armchair, to borrrow a phrase from Frank: You are mixing apples and oranges. It's good that you are reading Litz's book, but it does nothing for the discussion on this Thread to keep quoting different parts of it verbatim for the simple purpose of repeatedly announcing that I am wrong.
When I say the bullet gets less stable the farther it flies I am saying that the bullet, as it slows down, gets affected more and more by the external forces that are acting upon it. As a practical matter those forces are what we must concern ourselves with when we make our decisions.
Think about the application of what you are saying: Relevant to twist rate, if we made our decision according to the theory you quoted we would all get very slow twist barrels because we shoot very far. If you were correct, we wouldn't care about an initial Sg of 1.0 at the muzzle because we know that by the time the bullet gets to the target is has slowed enough to make the Sg a 1.7.
Of course we know that's not how it works: We need fast-twist barrels, and we use ever faster twists the slower the bullet ends-up... Because either a bullet is stable; or it isn't. </div></div>I'm not trying to take shots at you. It just appears to me that when I point something out you put some kind of spin on it and send it back my way. Look, I'm wrong quite a bit. I don't like being wrong but it's part of life and I learn from it and move on. In this case I think that some of the things you said were not correct and we could debate them indefinitely if we are both more interested in winning an argument than clarifying the truth. I've seen many of your posts and I'm well aware that you are a very intelligent person, but I still disagree. It's nothing personal.
I've already said what I intended to say so I don't feel the need to get into semantics. These discussions are supposed to be geared towards mutual instruction, learning and sharing of information. If you feel that I was simply attacking you instead of contributing to the conversation then I apologize. It was not my intention.
Re: Bullet "Settling/Laying Down" - Fact or Theory?
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Graham</div><div class="ubbcode-body">KY, I know what you are saying about gyroscopic stability - meaning that the velocity decreases faster than RPMs do. I don't dispute that.
I<span style="color: #000099"> see that you do, and I'm not trying to be argumentative. But I think part of what your wrote below could be confusing for someone who doesn't know how stability works. </span>
But...
Armchair, to borrrow a phrase from Frank: You are mixing apples and oranges. It's good that you are reading Litz's book, but it does nothing for the discussion on this Thread to keep quoting different parts of it verbatim for the simple purpose of repeatedly announcing that I am wrong.
When I say the bullet gets less stable the farther it flies I am saying that the bullet, as it slows down, gets affected more and more by the external forces that are acting upon it. As a practical matter those forces are what we must concern ourselves with when we make our decisions.
<span style="color: #000099"><span style="font-style: italic">With respect to stability</span>, it does <span style="font-style: italic">not</span> get affected more by external forces, it gets affected less, until it gets to the transition to subsonic, which is a whole other discussion on dynamic stability. For the benefit of those who may be confused by all of this back and forth, if a bullet has enough spin to by gyroscopically stable when it leaves the muzzle, it will only get more stable during flight, until it transitions to subsonic. It makes a successful transition to subsonic based on more factors than just spin, and that is really another subject.
</span>
Think about the application of what you are saying: Relevant to twist rate, if we made our decision according to the theory you quoted we would all get very slow twist barrels because we shoot very far. If you were correct, we wouldn't care about an initial Sg of 1.0 at the muzzle because we know that by the time the bullet gets to the target is has slowed enough to make the Sg a 1.7.
<span style="color: #000099">Hopefully everyone knows we need a stable bullet because if it tumbles the rest of the discussion is moot. Besides that though, our decision is very close to what you said here. For best accuracy we usually <span style="font-style: italic">do</span> choose the slowest twist we can to achieve at least an Sg of 1.0 (Litz suggests 1.4) at the muzzle because we know it will only get better from there.
</span>
Of course we know that's not how it works: We need fast-twist barrels, and we use ever faster twists the slower the bullet ends-up... Because either a bullet is stable; or it isn't.
<span style="color: #000099">We don't choose twist rates based on how slow the bullet will get. The twist we need is based on the length of the bullet and the environmentals (air density). Graham is right when he says we need fast twist barrels - but only because rifles used for long range are loaded with long for caliber, high BC bullets. Longer shapes need faster spins to stabilize. Thicker air, such as when it is cold, with low humidity, or you are at sea level, means than there is more overturning force on the bullet, so the very same bullet in those conditions needs more spin than the same bullet in conditions that produce less dense air: high altitude, humid, warm air.
There is one exception to the "choose just enough twist" convention that is really beyond the scope of the kind of shooting most long range shooters do. If you wish to engage targets at such a range that your bullet will be subsonic, then you need the bullet to make the sound barrier transition without becoming unstable. Many bullets do not transition well, because dynamic instability affects overcome gyroscopic stability in many cases. There is a possibility in some conditions you can increase the odds of a successful subsonic transition by increasing the spin rate. It may or may not work. .308 168SMKs in particular have a reputation for not doing well in the trans-sonic area, a problem extra twist does not appear to solve for that bullet.</span> </div></div>
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Graham</div><div class="ubbcode-body">KY, I know what you are saying about gyroscopic stability - meaning that the velocity decreases faster than RPMs do. I don't dispute that.
I<span style="color: #000099"> see that you do, and I'm not trying to be argumentative. But I think part of what your wrote below could be confusing for someone who doesn't know how stability works. </span>
But...
Armchair, to borrrow a phrase from Frank: You are mixing apples and oranges. It's good that you are reading Litz's book, but it does nothing for the discussion on this Thread to keep quoting different parts of it verbatim for the simple purpose of repeatedly announcing that I am wrong.
When I say the bullet gets less stable the farther it flies I am saying that the bullet, as it slows down, gets affected more and more by the external forces that are acting upon it. As a practical matter those forces are what we must concern ourselves with when we make our decisions.
<span style="color: #000099"><span style="font-style: italic">With respect to stability</span>, it does <span style="font-style: italic">not</span> get affected more by external forces, it gets affected less, until it gets to the transition to subsonic, which is a whole other discussion on dynamic stability. For the benefit of those who may be confused by all of this back and forth, if a bullet has enough spin to by gyroscopically stable when it leaves the muzzle, it will only get more stable during flight, until it transitions to subsonic. It makes a successful transition to subsonic based on more factors than just spin, and that is really another subject.
</span>
Think about the application of what you are saying: Relevant to twist rate, if we made our decision according to the theory you quoted we would all get very slow twist barrels because we shoot very far. If you were correct, we wouldn't care about an initial Sg of 1.0 at the muzzle because we know that by the time the bullet gets to the target is has slowed enough to make the Sg a 1.7.
<span style="color: #000099">Hopefully everyone knows we need a stable bullet because if it tumbles the rest of the discussion is moot. Besides that though, our decision is very close to what you said here. For best accuracy we usually <span style="font-style: italic">do</span> choose the slowest twist we can to achieve at least an Sg of 1.0 (Litz suggests 1.4) at the muzzle because we know it will only get better from there.
</span>
Of course we know that's not how it works: We need fast-twist barrels, and we use ever faster twists the slower the bullet ends-up... Because either a bullet is stable; or it isn't.
<span style="color: #000099">We don't choose twist rates based on how slow the bullet will get. The twist we need is based on the length of the bullet and the environmentals (air density). Graham is right when he says we need fast twist barrels - but only because rifles used for long range are loaded with long for caliber, high BC bullets. Longer shapes need faster spins to stabilize. Thicker air, such as when it is cold, with low humidity, or you are at sea level, means than there is more overturning force on the bullet, so the very same bullet in those conditions needs more spin than the same bullet in conditions that produce less dense air: high altitude, humid, warm air.
There is one exception to the "choose just enough twist" convention that is really beyond the scope of the kind of shooting most long range shooters do. If you wish to engage targets at such a range that your bullet will be subsonic, then you need the bullet to make the sound barrier transition without becoming unstable. Many bullets do not transition well, because dynamic instability affects overcome gyroscopic stability in many cases. There is a possibility in some conditions you can increase the odds of a successful subsonic transition by increasing the spin rate. It may or may not work. .308 168SMKs in particular have a reputation for not doing well in the trans-sonic area, a problem extra twist does not appear to solve for that bullet.</span> </div></div>
Re: Bullet "Settling/Laying Down" - Fact or Theory?
KY, you are correct about not choosing a twist rate based on the final downrange velocity of the bullet. After re-reading what I posted I see that I really didn't say that very well. What I meant to say by that, and what would have been clearer had I said it more accurately, is that we choose faster twist rates when the initial velocity of a given cartridge or load is slower, but we nevertheless intend to shoot it at the same long range -like when using a short barrel in a .308 for example.
KY, you are correct about not choosing a twist rate based on the final downrange velocity of the bullet. After re-reading what I posted I see that I really didn't say that very well. What I meant to say by that, and what would have been clearer had I said it more accurately, is that we choose faster twist rates when the initial velocity of a given cartridge or load is slower, but we nevertheless intend to shoot it at the same long range -like when using a short barrel in a .308 for example.
Re: Bullet "Settling/Laying Down" - Fact or Theory?
No worries I figured that, I just didn't want any new guys to misunderstand. It can be a confusing subject, which is why I really appreciate this site and Litz's book.
No worries I figured that, I just didn't want any new guys to misunderstand. It can be a confusing subject, which is why I really appreciate this site and Litz's book.
Re: Bullet "Settling/Laying Down" - Fact or Theory?
Thanks for cleaning that up KY. It will be much easier to understand for someone reading the thread.
Thanks for cleaning that up KY. It will be much easier to understand for someone reading the thread.
Re: Bullet "Settling/Laying Down" - Fact or Theory?
I have heard of this issue (groups getting tighter with distance) all my working life. I have never seen it with my own eyes. In my experience once the bullet starts going "out" it does not come back to center line. If one discounts the effect of the wind I can't imagine what force would cause the group to tighten once there is angular displacement.
I have heard of this issue (groups getting tighter with distance) all my working life. I have never seen it with my own eyes. In my experience once the bullet starts going "out" it does not come back to center line. If one discounts the effect of the wind I can't imagine what force would cause the group to tighten once there is angular displacement.
