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Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
OVERSPIN ??? twist and bullet spin
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<blockquote data-quote="MagnumManiac" data-source="post: 907886" data-attributes="member: 10755"><p>Contrary to what most people take as gospel, the myth of over stabilized is just that, unless a ridiculous amount of twist is used. The most accurate twist is the one that just stabilizes the bullet at the desired velocity. A 1:13" twist in a 30cal above 3300fps for a 155gr bullet is ideal, it will not sufficiently spin a 180gr or heavier bullet to be stable unless it is a short RN design and the velocity is high.</p><p>A bullet that is spun too fast is still stable, as in bullet tip polnting to target and not wobbling around it's axis, but a high spin rate can cause the core to slip in the jacket resulting in total bullet break up. It also can cause poor groups due to any imperfections causing a slight yawing while it travels to the target. Another possibility is the bullet failing due to the jacket stripping the rifling, the starting and stopping of the spin causes the jacket to fail before the bullet leaves the barrel.</p><p>I witnessed this with Speer 125gr THT HP's fired from my 28" barreled 300WinMag, velocity would have been in excess of 3600fps, a fellow shooter informed me that a 'blue streak' was appearing about 25yrds from the muzzle and no holes were in the target, apart from some peppering from the shrapnel of the bullet jacket. I asked him to shoot the rifle so I could see the results for myself, yes, there was a blue streak downrange about 25yrds from the muzzle and molten lead was also seen on the targets at 50yrds.</p><p>A 1:8" twist is very fast in 30 cal, the srandard 1:10" twist serves very well for almost all bullet weights, including the 240gr SMK as long as the velocity is high enough.</p><p></p><p>Cheers.</p><p>gun)</p></blockquote><p></p>
[QUOTE="MagnumManiac, post: 907886, member: 10755"] Contrary to what most people take as gospel, the myth of over stabilized is just that, unless a ridiculous amount of twist is used. The most accurate twist is the one that just stabilizes the bullet at the desired velocity. A 1:13" twist in a 30cal above 3300fps for a 155gr bullet is ideal, it will not sufficiently spin a 180gr or heavier bullet to be stable unless it is a short RN design and the velocity is high. A bullet that is spun too fast is still stable, as in bullet tip polnting to target and not wobbling around it's axis, but a high spin rate can cause the core to slip in the jacket resulting in total bullet break up. It also can cause poor groups due to any imperfections causing a slight yawing while it travels to the target. Another possibility is the bullet failing due to the jacket stripping the rifling, the starting and stopping of the spin causes the jacket to fail before the bullet leaves the barrel. I witnessed this with Speer 125gr THT HP's fired from my 28" barreled 300WinMag, velocity would have been in excess of 3600fps, a fellow shooter informed me that a 'blue streak' was appearing about 25yrds from the muzzle and no holes were in the target, apart from some peppering from the shrapnel of the bullet jacket. I asked him to shoot the rifle so I could see the results for myself, yes, there was a blue streak downrange about 25yrds from the muzzle and molten lead was also seen on the targets at 50yrds. A 1:8" twist is very fast in 30 cal, the srandard 1:10" twist serves very well for almost all bullet weights, including the 240gr SMK as long as the velocity is high enough. Cheers. gun) [/QUOTE]
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OVERSPIN ??? twist and bullet spin
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