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Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
6.5mm twist rate
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<blockquote data-quote="Michael Courtney" data-source="post: 714612" data-attributes="member: 28191"><p>The more conservative estimates have you shooting the fastest twist you might possibly need: the longest bullet in the densest air (0 deg F, death valley, etc.).</p><p></p><p>The negatives of spinning too fast are small but real: increased spin drift, more barrel resistance engraving and spinning the bullet, possible lower BC due to rifling marks at a larger angle to flight direction, bullet tip lags a bit more aligning with direction of travel, etc.</p><p></p><p>Next time I buy a new 6.5 barrel I intend to carefully consider the altitudes and air densities I intend to use it at and buy the slowest twist needed to stabilize my preferred 140 grain match bullets. I can always shoot shorter, lighter bullets if I need to make a trip to lower elevations/higher air densities.</p><p></p><p>Just to give you an idea on how much you can get away with at higher elevations. My home range is at about 6400 ft elevation. I can stabilize a 69 grain match bullet from a 1 in 12" twist .223 Remington. I can also stabilize several other bullets that recommend 1 in 9" and 1 in 10" twist rates. At this elevation, a 1 in 10" twist will stabilize the 140 AMAX in 6.5, and a 1 in 9" twist will stabilize the 140 grain Berger VLD.</p></blockquote><p></p>
[QUOTE="Michael Courtney, post: 714612, member: 28191"] The more conservative estimates have you shooting the fastest twist you might possibly need: the longest bullet in the densest air (0 deg F, death valley, etc.). The negatives of spinning too fast are small but real: increased spin drift, more barrel resistance engraving and spinning the bullet, possible lower BC due to rifling marks at a larger angle to flight direction, bullet tip lags a bit more aligning with direction of travel, etc. Next time I buy a new 6.5 barrel I intend to carefully consider the altitudes and air densities I intend to use it at and buy the slowest twist needed to stabilize my preferred 140 grain match bullets. I can always shoot shorter, lighter bullets if I need to make a trip to lower elevations/higher air densities. Just to give you an idea on how much you can get away with at higher elevations. My home range is at about 6400 ft elevation. I can stabilize a 69 grain match bullet from a 1 in 12" twist .223 Remington. I can also stabilize several other bullets that recommend 1 in 9" and 1 in 10" twist rates. At this elevation, a 1 in 10" twist will stabilize the 140 AMAX in 6.5, and a 1 in 9" twist will stabilize the 140 grain Berger VLD. [/QUOTE]
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Rifles, Reloading, Optics, Equipment
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6.5mm twist rate
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