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Rifles, Reloading, Optics, Equipment
Reloading
Barrel length and twist rate
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<blockquote data-quote="QuietTexan" data-source="post: 2788097" data-attributes="member: 116181"><p>If the rifling is well cut and constant, there's no additional "influence" once the turn has started. It really only takes the length of the bullet bearing surface to gain the full twist imparted by the rifling. After that the bullet rides down the tracks engraved in the jacket by the lands. If anything a longer barrel has more opportunities to have the lands be cut unevenly, and that would do more damage to a bullet jacket than a shorter barrel that has fewer inconsistencies.</p><p></p><p>Bullets blowing up can be caused by multiple things. Very long bullets can twist before the entire bearing surface is engraved into the rifling lands. Very thin jackets can have a higher percentage of metal displaced away from the core. If either of those happen the bond between the core and jacket can break, and the bullet gets torn apart by its own off-axis forces after it leaves the barrel. Bond can mean both chemical bonding used in bonded bullets, or simply the frictional/interference fit between core and jacket.</p><p></p><p>An exception to all this is gain twist barrels, in those the bullet has to pass through the the fastest point of the rifling to have that spin imparted on it. If you cut a gain twist down the final twist won't be what was specified, it'll be somewhere between the two specs. If you look at bullets that come out of gain twists the rifling marks are wider than the lands because of constantly re-engraving during the twist. If the rate is correct and the bullet isn't designed too lightly there's no negative side effects to the wider (but not deeper) tracks. Since the bullet is continually re-engraving itself onto the lands there is a small energy loss, but seeing as how a primer alone can get some bullets so engraved they get stuck, it's a meaningless difference in the overall energy budget of the cartridge.</p></blockquote><p></p>
[QUOTE="QuietTexan, post: 2788097, member: 116181"] If the rifling is well cut and constant, there's no additional "influence" once the turn has started. It really only takes the length of the bullet bearing surface to gain the full twist imparted by the rifling. After that the bullet rides down the tracks engraved in the jacket by the lands. If anything a longer barrel has more opportunities to have the lands be cut unevenly, and that would do more damage to a bullet jacket than a shorter barrel that has fewer inconsistencies. Bullets blowing up can be caused by multiple things. Very long bullets can twist before the entire bearing surface is engraved into the rifling lands. Very thin jackets can have a higher percentage of metal displaced away from the core. If either of those happen the bond between the core and jacket can break, and the bullet gets torn apart by its own off-axis forces after it leaves the barrel. Bond can mean both chemical bonding used in bonded bullets, or simply the frictional/interference fit between core and jacket. An exception to all this is gain twist barrels, in those the bullet has to pass through the the fastest point of the rifling to have that spin imparted on it. If you cut a gain twist down the final twist won't be what was specified, it'll be somewhere between the two specs. If you look at bullets that come out of gain twists the rifling marks are wider than the lands because of constantly re-engraving during the twist. If the rate is correct and the bullet isn't designed too lightly there's no negative side effects to the wider (but not deeper) tracks. Since the bullet is continually re-engraving itself onto the lands there is a small energy loss, but seeing as how a primer alone can get some bullets so engraved they get stuck, it's a meaningless difference in the overall energy budget of the cartridge. [/QUOTE]
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Rifles, Reloading, Optics, Equipment
Reloading
Barrel length and twist rate
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