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Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
Relationship between CBTO and freebore demension
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<blockquote data-quote="cdherman" data-source="post: 2605483" data-attributes="member: 12282"><p>I really futzed over a COAL for a 7mm SAUM. Same basic quandry that all the folks with a SA have. BUT Boisedoc is building on a long. I would advocate that he should pick a couple bullets that he thinks are likely candidates for the application he desires, include one of a slightly lighter weight, and load up several dummy rounds with the main body of the bullet a proper .308 into the neck of the cartridge. That can be tricky, but manufacturers give you good diagrams and you can make marks with a caliper to find this.</p><p></p><p>Send the smith the shortest of these, measured to CBTO. Since you are measuring them all with the same tool, you measurements are internally consistent. You can always seat the longer bullets deeper, but you cannot seat a short bullet shallower, as your run out will start to rise. </p><p></p><p>Of course, if this a bench queen, you can do whatever you want. But the old wisdom (I know many disagree) is that a good rule of thumb is one bullet diameter into the neck.</p><p></p><p>The problems encountered with long action (cannot seat bullet to lands, too much jump) are often different that the SA world, where we hit box capacity far too soon. Too much free bore in a LA means you cannot tune the load. TOO LITTLE COAL in any action mean diminished case capacity and less velocity.</p></blockquote><p></p>
[QUOTE="cdherman, post: 2605483, member: 12282"] I really futzed over a COAL for a 7mm SAUM. Same basic quandry that all the folks with a SA have. BUT Boisedoc is building on a long. I would advocate that he should pick a couple bullets that he thinks are likely candidates for the application he desires, include one of a slightly lighter weight, and load up several dummy rounds with the main body of the bullet a proper .308 into the neck of the cartridge. That can be tricky, but manufacturers give you good diagrams and you can make marks with a caliper to find this. Send the smith the shortest of these, measured to CBTO. Since you are measuring them all with the same tool, you measurements are internally consistent. You can always seat the longer bullets deeper, but you cannot seat a short bullet shallower, as your run out will start to rise. Of course, if this a bench queen, you can do whatever you want. But the old wisdom (I know many disagree) is that a good rule of thumb is one bullet diameter into the neck. The problems encountered with long action (cannot seat bullet to lands, too much jump) are often different that the SA world, where we hit box capacity far too soon. Too much free bore in a LA means you cannot tune the load. TOO LITTLE COAL in any action mean diminished case capacity and less velocity. [/QUOTE]
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Relationship between CBTO and freebore demension
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