Is it possible for a rifle to be more accurate at distance than 100 yards?
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denton
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OK, here are the results of my ballistic software comparisons.
I had never paid much attention to which drag function to use, until now. Wreck-n-Crew is correct that we should use the G1 drag function for the flat base bullet, and the G7 (or possibly G5) for the boat tail. So I have simplified things by using only the correct drag function on each bullet.
The Sierra numbers are courtesy of Bart B. I neglected to ask him for G1 with the round nose, so we don't have that data yet.
Some of the software does not permit choice of G1 and G7. For that reason, I just deleted the Nosler app from my phone. Strelok is next.
Here are the numbers:
I had never paid much attention to which drag function to use, until now. Wreck-n-Crew is correct that we should use the G1 drag function for the flat base bullet, and the G7 (or possibly G5) for the boat tail. So I have simplified things by using only the correct drag function on each bullet.
The Sierra numbers are courtesy of Bart B. I neglected to ask him for G1 with the round nose, so we don't have that data yet.
Some of the software does not permit choice of G1 and G7. For that reason, I just deleted the Nosler app from my phone. Strelok is next.
Here are the numbers:
Snyper
Member
A spinning top is actually rolling on a flat surface, not flying through the air.
A bullet doesn't spiral around some center line in ever tightening circles.
When that term is used it's referring to the nose of the projectile only
Snyper
Member
Exactly.
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Snyper
Member
I don't think you understand that still doesn't prove a particular rifle will shoot a smaller group at a farther distance than it will at 100 yards.
You keep "proving" things no one but you has mentioned.
The first paragraph of your "proof" says:
As I asked before, please copy and paste the specific portion that "proves" smaller groups at longer range compared to the group produced at 100 yards.
Bryan Litz is looking for you to prove it by shooting such groups.
You'll be better off understanding all the supporting facts why slower bullets leaving the barrel at higher angles above the line of sight will have a greater maximum ordinate than faster ones a little past mid range so both trajectories cross at target range.
The best proof is in the trajectory pictures I posted. Their separation will be smaller at short range. Slower bullets are shown leaving at a higher angle than faster ones. Benchrest rifles often have weights on barrel muzzles to change the frequency the muzzle axis vibrates at so bullets leave at optimum angles for their velocity so they'll converge down range at the target, then diverge past the target.
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As a matter of fact it does. The physics behind this have been repeated ad nauseum in this thread (and numerous others over the past decades) and the interaction between the supporting force of a table surface vs. gravity acting on the (rotating) mass of the top doesn't differ from the decelerating force of wind resistance vs. velocity momentum of the bullet. As the initial disturbance of balance diminishes in the function of time that gyroscopic force acts on the bullet (or top, for that matter), the angle and distance between rotational axis and center axis of circular motion diminishes as well.
So, the theory and explanation according to laws of physics is definitely there. From that point on it's up to further empirical research to confirm that this particular effect has causality between observed and repeatable discrepancy in relative accuracy at different distances.
Until someone bothers to do it, this is just a theory, but lacking a better one it seems quite plausible. Unless blanket claims that everyone who has observed the phenomenon and been able to repeat it with reasonable consistency is just full of manure are regarded as such, of course. That's the easiest way to brush it off without needing to think about it any further.
I've got zero's at 100 yards with two 308 Win rifles, one barreled for heavier (168 to 190's) bullets, the other for light (155's) chronographing them noting atmosphere conditions. Used Sierra's software to calculate zero's for 600, 800 and 1000 yards. Calculated zero's versus long range tests' zeros were within 1/2 MOA at all ranges; probably due to slight atmosphere variables in trajectories compared to what was measured at the firing point. Proof to me Sierra's software is good for their bullets.
Aperture sights were used as their click values for the two rifle's different sight radii were easily calculated to several decimal places. Scopes are harder to determine exact movement per click. But that's another thread.
Aperture sights were used as their click values for the two rifle's different sight radii were easily calculated to several decimal places. Scopes are harder to determine exact movement per click. But that's another thread.
denton
Member
OK.... this discussion has caused me to do some digging. Here is my report:
My main source is Harold Vaughn's Rifle Accuracy Facts. Harold was in charge of handling the fluid dynamics computations for our country's ICBMs, and he held a doctorate in the field. He was also a hard-core experimentalist, dragging a big old Tektronix 555 oscilloscope (I had one of those once.) and gas generator into the field to make measurements. If you want to understand how his work is regarded, try buying a used copy somewhere.
Question 1: Does the nose of the bullet trace out a spiral as the bullet flies? Yes. Harold developed software that accurately models the situation. The software is capable of six degrees of freedom, i.e., it handles position in three dimensions and angles in three dimensions. Here is one of the graphs he produced.
Question 2. Does this cause the bullet to corkscrew around its trajectory? Yes. It must be so, because the drag vector always points from tip to center of base, and when the bullet nose does not point exactly forward, the drag vector has a transverse component that moves the bullet sideways and up and down. Fluid dynamics substantially changes the situation, vs. ballistics in a vacuum.
From page 182:
The initial angle of attack of .2 degrees was chosen because it is probably typical of the maximum initial angle of attack that would be present in a good rifle with a chamber and throat on the center of the bore....Of course the bullet is flying along a cork screw trajectory around the average flight path. The effect of the cork screw motion on dispersion is considered later.
Question 3. Is this effect important to most of us? No. From page 192:
So what are the practical effects of GS [gyroscope stability] on accuracy? Well it is important to realize that the bullet is traveling in a corkscrew motion about the trajectory when it is coning...For a .2 degree angle of attack the radius of the corkscrew motion will be about .009 inches for a GS of 2.98. By the time the bullet reaches 200 yards the angular motion has damped so that the radius of the corkscrew motion is only .003 inches.
Bryan Litz's money is probably safe unless someone with a lot of patience and a superbly accurate rail gun chooses to compete for it.
How else can a rifle appear to be substantially more accurate at 200 yards than at 100? I can think of two good explanations:
1. Scope parallax. It is at least conceivable that this might be a factor.
2. Failure to understand the statistics of comparing group sizes. Suffice it to say that if you shoot a 1" 5-shot group at 100 yards, then a 1.5" 5-shot group at 200 yards, you definitely do NOT have convincing evidence of better accuracy at 200 yards. The two groups are samples, drawn from a large population, and an outcome like this is easily possible just by normal random variation.
My main source is Harold Vaughn's Rifle Accuracy Facts. Harold was in charge of handling the fluid dynamics computations for our country's ICBMs, and he held a doctorate in the field. He was also a hard-core experimentalist, dragging a big old Tektronix 555 oscilloscope (I had one of those once.) and gas generator into the field to make measurements. If you want to understand how his work is regarded, try buying a used copy somewhere.
Question 1: Does the nose of the bullet trace out a spiral as the bullet flies? Yes. Harold developed software that accurately models the situation. The software is capable of six degrees of freedom, i.e., it handles position in three dimensions and angles in three dimensions. Here is one of the graphs he produced.
Question 2. Does this cause the bullet to corkscrew around its trajectory? Yes. It must be so, because the drag vector always points from tip to center of base, and when the bullet nose does not point exactly forward, the drag vector has a transverse component that moves the bullet sideways and up and down. Fluid dynamics substantially changes the situation, vs. ballistics in a vacuum.
From page 182:
The initial angle of attack of .2 degrees was chosen because it is probably typical of the maximum initial angle of attack that would be present in a good rifle with a chamber and throat on the center of the bore....Of course the bullet is flying along a cork screw trajectory around the average flight path. The effect of the cork screw motion on dispersion is considered later.
Question 3. Is this effect important to most of us? No. From page 192:
So what are the practical effects of GS [gyroscope stability] on accuracy? Well it is important to realize that the bullet is traveling in a corkscrew motion about the trajectory when it is coning...For a .2 degree angle of attack the radius of the corkscrew motion will be about .009 inches for a GS of 2.98. By the time the bullet reaches 200 yards the angular motion has damped so that the radius of the corkscrew motion is only .003 inches.
Bryan Litz's money is probably safe unless someone with a lot of patience and a superbly accurate rail gun chooses to compete for it.
How else can a rifle appear to be substantially more accurate at 200 yards than at 100? I can think of two good explanations:
1. Scope parallax. It is at least conceivable that this might be a factor.
2. Failure to understand the statistics of comparing group sizes. Suffice it to say that if you shoot a 1" 5-shot group at 100 yards, then a 1.5" 5-shot group at 200 yards, you definitely do NOT have convincing evidence of better accuracy at 200 yards. The two groups are samples, drawn from a large population, and an outcome like this is easily possible just by normal random variation.
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Good job. A worthy conclusion to a thread.
Jim Watson
Member
This is not a matter of whole number of inches on the target, is it?
It must have entered rehab at 125.
denton
Member
... .009 inches ...
I notice the effect quite often with my SKS.
I notice the effect quite often with my SKS.
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Snyper
Member
So you can't show it and just keep repeating the same thing.
Snyper
Member
If the "spiral" is measured in thousandths of an inch it's really a "wobble" rather than the entire bullet traveling in a corkscrew path around some imaginary line.
The speed of the rotation wouldn't allow the air time to force it in a different direction.
As you said, the theory is there, but I don't believe there's enough "spiral" to matter in the real world, and it still has nothing to do with "more accurate at longer range..."
I think most bullets stabilize before reaching 100 yards. Then their tip and base centers will spin around an axis parallel to the trajectory. Their center of mass will be on the trajectory axis, their tip and base on opposite sides of the trajectory by thousandths of an inch at most. That's assuming they're good bullets not unbalanced by loading and firing. Otherwise, the best of them would shoot under 1/4" at 100 yards.
The greater the bullet's shape axis angle is from the trajectory axis, the more drag it will have lowering its BC. It slows down more than perfectly balanced ones. Data supporting this phenomena is explained in my old Sierra manual with times of flight varying across a range band were not linear with the spread of entry velocity. The 1% to 2% spread in calculated G1 BC was attributed to bullet balance. As their amount of unbalance is constant throuout their trajectory stays constant, so will the size of the circle their tip and base centers spin around their trajectory axis.
Things get worse when such bullets go subsonic.
The greater the bullet's shape axis angle is from the trajectory axis, the more drag it will have lowering its BC. It slows down more than perfectly balanced ones. Data supporting this phenomena is explained in my old Sierra manual with times of flight varying across a range band were not linear with the spread of entry velocity. The 1% to 2% spread in calculated G1 BC was attributed to bullet balance. As their amount of unbalance is constant throuout their trajectory stays constant, so will the size of the circle their tip and base centers spin around their trajectory axis.
Things get worse when such bullets go subsonic.
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As you may now notice, that only contested your claim that it wasn't.
Jim Watson
Member
To talk about bullets "stabilizing" in mid-flight is a misnomer and a loaded term. If they weren't stable, they might not make it to a 100 yard target. All that is happening is that some of their irregular rotation is damping out. We have anecdotes that it can be so extreme and so regular as to cause trajectory convergence and we have calculations that show the "corkscrew" as much less than bullet diameter.
Just remembered watching bullets' trace going down range to 200, 300, 500 and 600 yard targets. When there's enough mirage (heat waves) in the bullets trajectory to see the bullets' trace disturbing that air refracting its light rays back to the spotting scope, one thing was constant across all of them. Past 50 to 70 yards, the trace for each was a very uniform arced path all the way to the target. No corkscrewing, spiraling, circling, whatsoever as viewed through 20 to 32 power spotting scopes. On some flat based bullets where sunlight was reflected back, it appeared as a bright spot flying down range at bullet speed; it never was anything but a perfectly shaped trajectory. If there were any corkscrew paths at all, they were too small to be seen
That, to me, dispels all the spiraling path often claimed to be how bullets fly down range.
That, to me, dispels all the spiraling path often claimed to be how bullets fly down range.
wally
Member
When a bullet leaves the muzzle it is stable to with a fraction of a caliber, otherwise baffle strikes with suppressors would be a way of life.
A .22lr can is approx 0.25" in its internal diameter. The exit hole in the end cap of my .30 cal suppressor is ~0.37" while the exit of my 5.56 suppressor is ~0.29" which proportionally larger, probably because the makers know folks will insist on shooting 77gr "match" bullets or 45gr "varmint" bullets through them that could be marginally stable depending on barrel twist and load velocity. Also some (most?) of the extra diameter may be to give margin for the tolerance associated with barrel bore and thread concentricity.
So are people now going to claim that the bullet gets less stable 12+ inches down range and then gets more stable much further down range?
Hand waving arguments about imagined mechanisms abound. The 6-DOF models seem to say it ain't happening. The author of one of the most advanced 6-DOF solvers says it ain't happening and has put up his money for a free all-expenses paid trip to his range/lab if you have a gun/ammo combination that can demonstrate it.
d2wing
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I do not think a bullet becomes more stable as it flies. It is at it's most stable when it leaves the muzzle unless there is a poor crown which would push the bullet base ever so slightly and could effect the path and wobble of the bullet. However this would not cause a bullet to change it's path or wobble down range. Wobble may decrease slightly but the path of the bullet would not change downrange or become more stable. Any deflection at the muzzle would continue to increase over time and distance. I think any effect that would increase accuracy downrange is that the target is smaller and the shooter takes a finer bead.
Do you think barrel vibrating frequencies don't change when their tuning weight at the front is moved back and forth?
Fleetman
Member
Maybe its just me but I get MUCH better groups at 300+ yards than 100 yards with my .50
olkowsr
Member
Rifle alone no... its literally a tube with some rifling that is "straight"....
Now paired with magnification and human operation, maybe....
Now paired with magnification and human operation, maybe....
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