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Old September 15, 2020, 03:59 PM   #26
Unclenick
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Join Date: March 4, 2005
Location: Ohio
Posts: 17,959
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 valley or 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 in the valley 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 is in addition to having a higher angle of departure. These will make the bullet impact higher than it would if it cleared the muzzle at an unmoving position at the 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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