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Old September 15, 2020, 03:59 PM   #26
Unclenick
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Quote:
Originally Posted by Nathan
How can “muzzle swing” impact external ballistics?
Most rifles have their barrel bore line axis above the point of stock contact on the shooter's shoulder. This causes a portion of the recoil to go into attempting to rotatate the rifle up and around the point of contact (it's what you see as muzzle rise). This cracks the whip on the barrel, resulting in the muzzle vibrating up and down, sinusoidally as shown in Mode 3 in the table of animations on this page. Like any sinusoidal motion, the rate of change in the muzzle's angle is greatest as it passes through zero deflection or value between the extremes of the swing range, and slowest near the extremes of the swing. If you time the bullet to get out near a peak, you can pick a slope in the rate of change that tends to compensate for small velocity variations.

The mechanism for that compensation is that if a slower bullet clears the muzzle when it is on the upswing, the velocity of the momentum the bullet picks up in that upswing will go the bullet as an upward vertical addition to its initial vertical velocity component that gravity and drag must overcome before the bullet reaches apogee and starts to fall. This will make the bullet impact higher than it would if it cleared the muzzle at an unmoving position at the top or bottom corner of the swing with no vertical motion (the static phase of the oscillation). So, if you can get the average bullet out at the right moment in the swing, such that faster bullets carry less upswing velocity and slow bullets carry more, they can all land at the same poi at some range at which the trajectories cross over one another and for a good distance before and after the crossover point if the lines don't diverge too fast. All the above is why barrel tuners shrink groups, regardless of exact load specifics.
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Old September 15, 2020, 07:27 PM   #27
Bart B.
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Unclenick, I don't understand how the muzzle axis angular rate of change upward being at right angles to the LOF increases bullet velocity.

With tuners set correct, the LOF angular rate of change is faster for the higher bullet velocities, slower for lowest velocities.

Last edited by Bart B.; September 15, 2020 at 08:38 PM.
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Old September 15, 2020, 07:45 PM   #28
mehavey
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Centrifugal force literally "flings" the bullet outward -- some small amount of added velocity.

(by my calculation:
- Average of 0.033 pounds of "fling" force
- on a 150gr bullet
- in a 2-ft barrel
- muzzle rotating upward at 10ft/sec recoil during bullet transit)

Last edited by mehavey; September 16, 2020 at 11:29 AM.
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Old September 16, 2020, 01:42 PM   #29
Bart B.
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Quote:
Originally Posted by mehavey View Post
Centrifugal force literally "flings" the bullet outward -- some small amount of added velocity
Does the barrel's recoil velocity subtract from that "fling" velocity?
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Old September 16, 2020, 02:39 PM   #30
mehavey
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Don't get picky.
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