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Rifles, Reloading, Optics, Equipment
Reloading
LEE press cant get same oal
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<blockquote data-quote="Bart B" data-source="post: 1154878" data-attributes="member: 5302"><p>The most accurate one would measure at a point on the bullet where it first touches the rifling relative to the case head. But that would vary depending on the chamber dimensions as well as the bullet dimensions. Any diameter smaller than bore diameter would be meaningless. And there's a spread of a couple thousandths in bore and groove diameters.</p><p></p><p>For example, a Sierra 30 caliber bullet of .3082" diameter with a 6 caliber ogive will touch the rifling in a SAAMI spec chamber at a diameter of about .305" to .306" at a point about 2.2" forward of the case head. If any other chamber dimension is used, that contact point will differ; especially with different throat/leade angles; the .308 Win spec is 1.5 degrees. 30 caliber chamber leade angles range from 1 to over 2 degrees and their bullet diameters range from .306" to .309"</p><p></p><p>But that's not what really happens with cases headspacing on their shoulders. There's a few thousandths spread from case head to some reference diameter on such case shoulders. When fired, the case shoulder is hard against the chamber shoulder so there's a few thousandths spread in head clearance from the bolt face to case head. The reference diameter on the bullet will move back and forth the same amount. Therefore, if every loaded round has zero spread in case head to bullet ogive reference, that spread in case headspace will be the same spread in how far the bullet has to jump to the rifling.</p><p></p><p>Whatcha gonna do about that? I don't do anything. A .005" spread in bullet jump to the rifling is meaningless unless you shoot your stuff no worse than 2/10ths MOA at short range. Then reduce it to a .001" spread; if you can.</p><p></p><p>The barrel's rifling erodes away .001" for every 5 to 40 rounds fired; depends on how much powder's burned for the bore size. Bullet jump increases that much if CBTO is constant.</p></blockquote><p></p>
[QUOTE="Bart B, post: 1154878, member: 5302"] The most accurate one would measure at a point on the bullet where it first touches the rifling relative to the case head. But that would vary depending on the chamber dimensions as well as the bullet dimensions. Any diameter smaller than bore diameter would be meaningless. And there's a spread of a couple thousandths in bore and groove diameters. For example, a Sierra 30 caliber bullet of .3082" diameter with a 6 caliber ogive will touch the rifling in a SAAMI spec chamber at a diameter of about .305" to .306" at a point about 2.2" forward of the case head. If any other chamber dimension is used, that contact point will differ; especially with different throat/leade angles; the .308 Win spec is 1.5 degrees. 30 caliber chamber leade angles range from 1 to over 2 degrees and their bullet diameters range from .306" to .309" But that's not what really happens with cases headspacing on their shoulders. There's a few thousandths spread from case head to some reference diameter on such case shoulders. When fired, the case shoulder is hard against the chamber shoulder so there's a few thousandths spread in head clearance from the bolt face to case head. The reference diameter on the bullet will move back and forth the same amount. Therefore, if every loaded round has zero spread in case head to bullet ogive reference, that spread in case headspace will be the same spread in how far the bullet has to jump to the rifling. Whatcha gonna do about that? I don't do anything. A .005" spread in bullet jump to the rifling is meaningless unless you shoot your stuff no worse than 2/10ths MOA at short range. Then reduce it to a .001" spread; if you can. The barrel's rifling erodes away .001" for every 5 to 40 rounds fired; depends on how much powder's burned for the bore size. Bullet jump increases that much if CBTO is constant. [/QUOTE]
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Reloading
LEE press cant get same oal
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