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Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
A Question for Warren
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<blockquote data-quote="Warren Jensen" data-source="post: 21096" data-attributes="member: 21"><p>Blaine,</p><p></p><p>It is 0620 hrs, Wed. 9/12/01. Yesterday was a bad day. All of our lives in one form or another will be changed permanently.</p><p></p><p>Back to the muzzle gas flow question. There are two things we know for sure. One is that the gas just in front of the bullet as it nears the muzzle is traveling at nearly the same speed as the bullet. Two is that at some distance of inches, maybe 2"-10", the front of the bullet will encounter clean, undisturbed air and normal flight airflow and shockwaves will ensue. The question is what happens in between these two events. I believe that a large number of different things can and does occur with different loads, bullets, pressures, velocities, and muzzles. </p><p></p><p>I am only discussing muzzles that are not vented, braked, suppressed, or the vent gases mechanically stripped. </p><p></p><p>As the bullet exits the muzzle and the seal is broken the pressure can vary from 1000-8000 psi., depending upon the load and pressure curve. This gas will then accelerate past the base of the bullet. The bullet is transitioning from rotating around the center of form dictated to it by the bore and grooves to rotating around it's center of mass. There will always be some amount of yaw and wobble here causing the base to offset from bore centerline. As the gas is accelerating past it will amplify this offset from a little to a lot. This is the muzzle jump wobble that you hear so much about and it is caused by events at the rear of the bullet, primarily, not the front. As the gas accelerates past the bullet it's pressure and velocity is dissipating very rapidly. In short, round nosed bullets from loads with very high vent gas pressures the gases can disturb the air in front of the bullet causing turbulence. Short round nosed bullets will have the highest Stability Factors and will be the least effected by turbulence. With long ogived bullets from loads with lower vent gas pressures I do not believe the gases measureably disturb the air in front of the bullet's nose. They are deflected to the side at some angle and any envelopment around the nose would be so dissipated as to be of little effect. The concept that this would be laminar flow is incorrect, in my opinion. The bullet is gyroscopically stabilized and it is the oncoming clean air that introduces the overturning moment. So until it encounters clean air the bullet has little destabilizing forces acting on it from the front. It is the rear where the cause of the yaw and wobble is initiated.</p><p></p><p>As for there being a fireball that the bullet flies through, I doubt it. That would require burning or unburnt powder to accelerate past the base to the nose and I am very dubious of any circumstances in which this would occur.</p><p></p><p>[ 09-12-2001: Message edited by: Warren Jensen ]</p><p></p><p>[ 09-12-2001: Message edited by: Warren Jensen ]</p></blockquote><p></p>
[QUOTE="Warren Jensen, post: 21096, member: 21"] Blaine, It is 0620 hrs, Wed. 9/12/01. Yesterday was a bad day. All of our lives in one form or another will be changed permanently. Back to the muzzle gas flow question. There are two things we know for sure. One is that the gas just in front of the bullet as it nears the muzzle is traveling at nearly the same speed as the bullet. Two is that at some distance of inches, maybe 2"-10", the front of the bullet will encounter clean, undisturbed air and normal flight airflow and shockwaves will ensue. The question is what happens in between these two events. I believe that a large number of different things can and does occur with different loads, bullets, pressures, velocities, and muzzles. I am only discussing muzzles that are not vented, braked, suppressed, or the vent gases mechanically stripped. As the bullet exits the muzzle and the seal is broken the pressure can vary from 1000-8000 psi., depending upon the load and pressure curve. This gas will then accelerate past the base of the bullet. The bullet is transitioning from rotating around the center of form dictated to it by the bore and grooves to rotating around it's center of mass. There will always be some amount of yaw and wobble here causing the base to offset from bore centerline. As the gas is accelerating past it will amplify this offset from a little to a lot. This is the muzzle jump wobble that you hear so much about and it is caused by events at the rear of the bullet, primarily, not the front. As the gas accelerates past the bullet it's pressure and velocity is dissipating very rapidly. In short, round nosed bullets from loads with very high vent gas pressures the gases can disturb the air in front of the bullet causing turbulence. Short round nosed bullets will have the highest Stability Factors and will be the least effected by turbulence. With long ogived bullets from loads with lower vent gas pressures I do not believe the gases measureably disturb the air in front of the bullet's nose. They are deflected to the side at some angle and any envelopment around the nose would be so dissipated as to be of little effect. The concept that this would be laminar flow is incorrect, in my opinion. The bullet is gyroscopically stabilized and it is the oncoming clean air that introduces the overturning moment. So until it encounters clean air the bullet has little destabilizing forces acting on it from the front. It is the rear where the cause of the yaw and wobble is initiated. As for there being a fireball that the bullet flies through, I doubt it. That would require burning or unburnt powder to accelerate past the base to the nose and I am very dubious of any circumstances in which this would occur. [ 09-12-2001: Message edited by: Warren Jensen ] [ 09-12-2001: Message edited by: Warren Jensen ] [/QUOTE]
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