Accuracy question

np307 said:
Wow. Wow. There is so much going on here I don't even know where to begin.

1) To address the point about a 'horizontal velocity component.' We need to understand a few things. First of all, IF it were true that your moving the barrel imparted acceleration on the bullet laterally, it would produce a curve, not a straight line. The acceleration produced by gravity results in a curve, and acceleration laterally (wind drift, etc.) produces a curve as well. There is not a scenario where the bullet could move off the bore axis without moving in a curve.
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Let's back up to basics here. A VELOCITY component does not impart a curve. An ACCELERATION (your word not mine) would. You've heard of vectors, right? What I have been saying is that if the muzzle is moving laterally when the bullet leaves it, the bullet will have an additional lateral component to it's velocity. It will not travel directly in line with the bore axis but will leave the muzzle at an angle as referenced to where the muzzle was and bore axis was pointing when it left.

It's pretty basic stuff. Sorry that there seems to be some desire to turn this into a pissing match.

As far as for the rest of your post I found it helpful, thank you. Regarding #4 I am seeing the wobble in the crosshairs on the target. I don't see how it could in reality be any more or less.
 
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Flashpoint said:
Let's back up to basics here. A VELOCITY component does not impart a curve. An ACCELERATION (your word not mine) would. You've heard of vectors, right? What I have been saying is that if the muzzle is moving laterally when the bullet leaves it, the bullet will have an additional lateral component to it's velocity. It will not travel directly in line with the bore axis but will leave the muzzle at an angle as referenced to where the muzzle was and bore axis was pointing when it left.

It's pretty basic stuff. Sorry that there seems to be some desire to turn this into a pissing match.
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Misunderstanding about what is acceleration and velocity aside, my point still stands that the bullet is not going to jump off line of the bore. It will travel in that direction. Read the other three points to understand what's going on there.
 
np307 said:
Misunderstanding about what is acceleration and velocity aside, my point still stands that the bullet is not going to jump off line of the bore. It will travel in that direction. Read the other three points to understand what's going on there.
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On that you are correct. :) I was a little late but please refer back to what I added to my last post.
 
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Flashpoint said:
What I have been saying is that if the muzzle is moving laterally when the bullet leaves it, the bullet will have an additional lateral component to it's velocity.
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That would be true if in fact the bullet was not rotating along it's axis of travel, which negates the effect of lateral influence on departure. It's the primary reason for the effectiveness of rifling.

Carry on.
 
Matt.Cross said:
That would be true if in fact the bullet was not rotating along it's axis of travel, which negates the effect of lateral influence on departure. It's the primary reason for the effectiveness of rifling.

Carry on.
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I hope you're kidding!
 
Flashpoint said:
On that you are correct. :) I was a little late but please refer back to what I added to my last post.
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I see that now. For clarity, the movement of the barrel would be acceleration. The bullet would experience said acceleration while in the barrel. Upon exiting the barrel, the bullet would no longer be experiencing that acceleration.

All of what takes place in the barrel is beyond negligible. You would not impart enough acceleration on the projectile to change the vector. You're talking about way too short of a period of time for that acceleration to significantly alter the flight path of the bullet.
 
JBoyette said:
True, but the level of affect is very small to poor aiming.
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John,
I'm not marginalizing you in the slightest.

I agree with you, BUT,

I will say that those of us that are fortunate to have their rigs tuned in and don't have to compensate for mechanical deficiencies are past the harmonic variables.

I have lived barrel harmonics and the pic below shows some of my groups tuning in a FAL 58.

It did not group well with the original muzzle device. I tried several types / kinds of muzzle devices all of which did in fact effect barrel harmonics. The last one I tried is a 3 finger Flash Hider and it started grouping Much Better, shown on left bulls eye.



4.10.16 , 58 brakes & grain_a.jpg
 
np307 said:
I see that now. For clarity, the movement of the barrel would be acceleration. The bullet would experience said acceleration while in the barrel. Upon exiting the barrel, the bullet would no longer be experiencing that acceleration.

All of what takes place in the barrel is beyond negligible. You would not impart enough acceleration on the projectile to change the vector. You're talking about way too short of a period of time for that acceleration to significantly alter the flight path of the bullet.
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We know that barrel harmonics have a material effect, and barrel harmonics are simply movement of the barrel while the bullet is in the barrel. Why would other lateral acceleration of the barrel have a negligible effect?
 
np307 said:
I see that now. For clarity, the movement of the barrel would be acceleration. The bullet would experience said acceleration while in the barrel. Upon exiting the barrel, the bullet would no longer be experiencing that acceleration.
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This is all correct, but is nothing new to me. :)

All of what takes place in the barrel is beyond negligible. You would not impart enough acceleration on the projectile to change the vector. You're talking about way too short of a period of time for that acceleration to significantly alter the flight path of the bullet.
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This if true is exactly what I'm looking for and was the main question and reason I wrote this post. Thank you.
 
JimB said:
We know that barrel harmonics have a material effect, and barrel harmonics are simply movement of the barrel while the bullet is in the barrel. Why would other lateral acceleration of the barrel have a negligible effect?
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That's actually in line with my point. Barrel harmonics don't produce differences in POI due to acceleration of the barrel imparting a different vector on the projectile. It produces differences in POI due to slight shifts in the actual position of the muzzle at the time the bullet leaves the barrel. Which is exactly what I was talking about the whole time. In the OP's scenario, the bullet isn't pushed off course by the movement of the barrel, or forces occurring between trigger pull and bullet exiting the muzzle. His POI is off because the muzzle itself is pointing farther away than he realizes.
 
np307 said:
That's actually in line with my point. Barrel harmonics don't produce differences in POI due to acceleration of the barrel imparting a different vector on the projectile. It produces differences in POI due to slight shifts in the actual position of the muzzle at the time the bullet leaves the barrel. Which is exactly what I was talking about the whole time. In the OP's scenario, the bullet isn't pushed off course by the movement of the barrel, or forces occurring between trigger pull and bullet exiting the muzzle. His POI is off because the muzzle itself is pointing farther away than he realizes.
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Maybe he just sucks at it.
 
Matt.Cross said:
You seem to have already agreed to statements to the exact same effect. Explain why my statement isn't sensible.
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I'm sorry I guess it would be easy to think that. The spin on a bullet produces a gyroscopic effect that resists changes in it's orientation, but not it's direction of travel. For example when figuring windage the spin rate is not considered, at least not in that capacity. A side wind is going to push a rotating mass just as far off it's path than it will a non-rotating mass, all else being equal.

OK maybe that wasn't the best example now that I think about it because there are aerodynamic effects the rotation has on wind so some long range calculations might include that, but my main point is that the spin resists changes in orientation, not changes in the flight path directly. Spin keeps bullets on track by keeping them pointed at a consistent angle downrange so their aerodynamics don't shove them off course. It also has the effect of equaling out imperfections in the bullet itself.
 
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np307 said:
That's actually in line with my point. Barrel harmonics don't produce differences in POI due to acceleration of the barrel imparting a different vector on the projectile. It produces differences in POI due to slight shifts in the actual position of the muzzle at the time the bullet leaves the barrel. Which is exactly what I was talking about the whole time. In the OP's scenario, the bullet isn't pushed off course by the movement of the barrel, or forces occurring between trigger pull and bullet exiting the muzzle. His POI is off because the muzzle itself is pointing farther away than he realizes.
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I agree that where the barrel is pointing is the greatest factor, and that where the barrel is pointing is often times not where the shooter thinks it is pointing for lots of reasons, some as complex as barrel harmonics and some as basic as breath control, trigger pull and posture.
 
np307 said:
They drop...in a parabolic curve
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Just for grins, can you think of two times when this statement is false. There are more than two.
 
JimB said:
Just for grins, can you think of two times when this statement is false. There are more than two.
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Well technically they don't in our atmosphere due to drag, not sure if that counts as one.

Wind deflection is one I can think of, more so vertical deflection caused by or updraft or something.

If the firing angle is downward would be another.
 
The Green Heron said:
If you drop a bullet beside the rifle, and fire the rifle in a dead level position into a theoretically limitless level range, which bullet hits the ground first?
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What caliber, and American or import ammo?
 
I love you science guys!

It's a parabolic arc if you are shooting away from the source of gravity, a curve implies that with the right circumstances the bullet could double back on itself.

Check that, upon reconsidering the problem with the drop of a bullet combined with it slowing due to resistance it does indeed curve.
 
np307 said:
Well technically they don't in our atmosphere due to drag, not sure if that counts as one.

Wind deflection is one I can think of, more so vertical deflection caused by or updraft or something.

If the firing angle is downward would be another.
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Atmospheric drag (excluding wind and other currents) would be constant, so wouldn't change the curve. I was thinking vertical, up or down as the most obvious, then updraft/downdraft, then changing air temp/density although that's pretty small I'd think. Changing angle either up or down would change the apex of the curve, but not it's shape.
 
JimB said:
Atmospheric drag (excluding wind and other currents) would be constant, so wouldn't change the curve. I was thinking vertical, up or down as the most obvious, then updraft/downdraft, then changing air temp/density although that's pretty small I'd think. Changing angle either up or down would change the apex of the curve, but not it's shape.
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Actually I had a long discussion with someone on another forum about POI shift changing when they were shooting over water. It was a pond and the shots were about 700 yards if I remember right. The humid air over the pond being less dense than surrounding atmospheric air pushed the POI up enough so that he missed the target. This was someone who was a good shooter and regularly shot at these distances.
 
JimB said:
I agree that where the barrel is pointing is the greatest factor, and that where the barrel is pointing is often times not where the shooter thinks it is pointing for lots of reasons, some as complex as barrel harmonics and some as basic as breath control, trigger pull and posture.
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I hear what you are saying and am not discounting it, however let me throw this out there: I was having issues with an AR a while back and put a ATN X-Sight scope on it which is basically a video camera with crosshairs because I wanted to see if I was jerking it off target. I could not see any additional movement in the video than I did through the scope, so I'm unclear on how the muzzle could be pointing somewhere the camera doesn't catch. Are you saying that I could be jerking it more than the video shows? BTW I was letting it free recoil.

FF to 5:35 for the shooting.

 
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np307 said:
Actually I had a long discussion with someone on another forum about POI shift changing when they were shooting over water. It was a pond and the shots were about 700 yards if I remember right. The humid air over the pond being less dense than surrounding atmospheric air pushed the POI up enough so that he missed the target. This was someone who was a good shooter and regularly shot at these distances.
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Isn't humid air more dense? It feels more dense. I hate humidity.
 
JimB said:
Isn't humid air more dense? It feels more dense. I hate humidity.
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No. That was one of the interesting points of the discussion. Water vapor has a density of like .97 if I remember right, and atmospheric air has a density of like 1.1 or something. I can't remember the exact numbers but it was a noticeable difference. I agree that it feels more dense.
 
Flashpoint said:
I hear what you are saying and am not discounting it, however let me throw this out there: I was having issues with an AR a while back and put a ATN X-Sight scope on it which is basically a video camera with crosshairs because I wanted to see if I was jerking it off target. I could not see any additional movement in the video than I did through the scope, so I'm unclear on how the muzzle could be pointing somewhere the camera doesn't catch. Are you saying that I could be jerking it more than the video shows? BTW I was letting it free recoil.
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Maybe, but I'd look at dirty barrel, loose chamber, bad crown, undersize ammo, etc if you can find no fault in your technique. Not to pimp for the instructors, but this is where professional observation can really pay off.
 
JimB said:
Maybe, but I'd look at dirty barrel, loose chamber, bad crown, undersize ammo, etc if you can find no fault in your technique. Not to pimp for the instructors, but this is where professional observation can really pay off.
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I'm sure it does. I'm not really having any issues right now, I don't own that AR anymore and I'm shooting as well as can be expected with my FV-SR right now. This is purely academic, until some day I get frustrated again ;) and then I'll consider just that.
 
Flashpoint said:
Spin keeps bullets on track by keeping them pointed at a consistent angle downrange so their aerodynamics don't shove them off course. It also has the effect of equaling out imperfections in the bullet itself.
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Exactly my meaning. If you model the inertia of your lateral movement as a vector acting as inertial influence on the mass of the projectile, you'll immediately realize that the scale of that vector is miniscule in comparison to the scale of the vectors of rotation and direction of travel. So much so that an equivalent deformation in the projectile would be overcome by the dynamic you just stated. Your lateral movement would have to be incredibly significant in it's velocity component before you could generate enough inertia to overwhelm the stability resulting from the combined vectors of acceleration and rotation.
 
Matt.Cross said:
Exactly my meaning. If you model the inertia of your lateral movement as a vector acting as inertial influence on the mass of the projectile, you'll immediately realize that the scale of that vector is miniscule in comparison to the scale of the vectors of rotation and direction of travel. So much so that an equivalent deformation in the projectile would be overcome by the dynamic you just stated. Your lateral movement would have to be incredibly significant in it's velocity component before you could generate enough inertia to overwhelm the stability resulting from the combined vectors of acceleration and rotation.
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Let's try to simplify, tell me if we're saying different things.
You're on a magic carpet traveling through space in a line at a constant velocity of 1000 m/s.
You point your rifle perfectly perpendicular to the direction that the magic carpet is traveling, but in the same horizontal plane.
I am standing on the ground and as you you pass over me you fire a round at 1,500 m/s.
I have super vision and watch the bullet, it leaves the gun and stays pointed parallel to the barrel, but it is traveling both away from the magic carpet at 1,500 m/s and parallel to the magic carpet at 1,000 m/s. It is traveling in a direction that is not the axis of the bullet.

The spin of the bullet keeps the axis of the bullet from changing, but does nothing to affect other forces acting on the bullet, in this case the velocity imparted by the magic carpet.

The more real world example would be that the spin of the bullet doesn't reduce the effect of wind on the bullet, the bullet heads off at an angle to the bore of the gun in a strong crosswind, but the axis of the bullet remains parallel to the bore.
 
JimB said:
Let's try to simplify, tell me if we're saying different things.
You're on a magic carpet traveling through space in a line at a constant velocity of 1000 m/s.
You point your rifle perfectly perpendicular to the direction that the magic carpet is traveling, but in the same horizontal plane.
I am standing on the ground and as you you pass over me you fire a round at 1,500 m/s.
I have super vision and watch the bullet, it leaves the gun and stays pointed parallel to the barrel, but it is traveling both away from the magic carpet at 1,500 m/s and parallel to the magic carpet at 1,000 m/s. It is traveling in a direction that is not the axis of the bullet.

The spin of the bullet keeps the axis of the bullet from changing, but does nothing to affect other forces acting on the bullet, in this case the velocity imparted by the magic carpet.

The more real world example would be that the spin of the bullet doesn't reduce the effect of wind on the bullet, the bullet heads off at an angle to the bore of the gun in a strong crosswind, but the axis of the bullet remains parallel to the bore.
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Hum, the movie is better,

 
The Green Heron said:
If you drop a bullet beside the rifle, and fire the rifle in a dead level position into a theoretically limitless level range, which bullet hits the ground first?
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The one dropped beside the rifle because of coriolis effect and barrel twist will cause the bullet to want to rise to the right. But only if you're shooting east. If you're shooting magnetic east then they ahould be the same plus or minus two seconds.
 
billyh said:
The one dropped beside the rifle because of coriolis effect and barrel twist will cause the bullet to want to rise to the right. But only if you're shooting east. If you're shooting magnetic east then they ahould be the same plus or minus two seconds.
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Seconds??? You obviously meant to say milliseconds when trying to add in coriolis effects. Everyone knows that's how it's measured...

You beach folks. Geez
 
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