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User Panel
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Posted: 10/21/2014 8:34:30 AM EDT
[#1]
Bullets need a minimum spin rate (RPM) for given conditions (air density) to stabilize.
Velocity and twist determine bullet RPM. |
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Posted: 10/21/2014 8:50:49 AM EDT
[#2]
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Posted: 10/21/2014 10:05:40 AM EDT
[#3]
With their shape, pointy at the front and heavy at the back they tend to want to swap ends (like a Porsche 911). You need to spin them fast enough to keep them pointing straight.
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Posted: 10/21/2014 11:26:11 PM EDT
[#4]
So if I am getting this right, muzzle velocity has some effect on gyroscopic stability (increased velocity down the barrel equals increased spin speed regardless of twist rate) but not as much effect as barrel twist rate. Also, as distance downrange increases and bullet velocity decreases, gyroscopic stability also decreases. Does that sound right?
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Posted: 10/22/2014 1:28:39 AM EDT
[#5]
Pretty much.
That's why at extended ranges, bullets tend to become less stable and can even tumble as they drop below trans-sonic. |
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Posted: 10/22/2014 7:44:15 AM EDT
[#6]
AFAIK bullet velocity only affects spin rate while in contact with the rifling.
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Posted: 10/23/2014 12:46:09 PM EDT
[#7]
Quote HistoryQuoted:
So if I am getting this right, muzzle velocity has some effect on gyroscopic stability (increased velocity down the barrel equals increased spin speed regardless of twist rate) but not as much effect as barrel twist rate. Also, as distance downrange increases and bullet velocity decreases, gyroscopic stability also decreases. Does that sound right? Increasing muzzle velocity increases bullet spin, and spin provides the stability. |
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Posted: 10/23/2014 12:50:41 PM EDT
[#8]
Quote HistoryQuoted:
AFAIK bullet velocity only affects spin rate while in contact with the rifling. True, but the external forces on a bullet change greatly as it goes from super to subsonic, which can lead to instability. Standard 5.56 loads will often tumble within 1000yd regardless of twist. |
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