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Rifles, Reloading, Optics, Equipment
Reloading
Case Cocentricity
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<blockquote data-quote="Clark" data-source="post: 243642" data-attributes="member: 6600"><p>The brass comes concentric when new.</p><p></p><p>The expander ball does .004" of bending if used in the same step as when the brass is sized, but much less if the brass is already sized.</p><p>The expander ball can be used later to bell the mouth of the case for cast bullets with little effect on concentricity.</p><p></p><p>That is, if the expander ball is removed, the brass sized, the expander ball replaced, the case inserted into the die only far enough for the neck to be expanded but not sized, then the ball is not pulling when expanding, but pushing.</p><p></p><p>The reason for the big difference between pushing and pulling with the expander ball is that pushing against a shell holder is more balanced than pulling. If the shell holder is open on one side, that side hangs back in pulling and the neck is bent toward that side.</p><p></p><p>In forming 6mmPPC brass from 220Russian, a mandrel is used and never an expander. I did not under stand the difference and wrote professor Bradshaw [assistant professor back in 1994]</p><p><a href="http://groups.google.com/group/rec.guns/browse_thread/thread/cb47be1a540f911e?hl=en&ie=UTF-8&q=Toby+Bradshaw+6mm+PPC+ball#b7facc7549be0ea5" target="_blank">Load development in a benchrest rifle - rec.guns | Google Groups</a></p><p></p><p>The answer was pushing vs pulling.</p><p></p><p></p><p>Here is Bart Bobbit telling me how he made his own concentricity gauge:</p><p><a href="http://groups.google.com/group/rec.guns/browse_thread/thread/cab7ebc55b06c585?hl=en&q=mandrel+group:rec.guns+author:clark#9c65408c14e34ad3" target="_blank">Setting up a concentricity checker. - rec.guns | Google Groups</a></p></blockquote><p></p>
[QUOTE="Clark, post: 243642, member: 6600"] The brass comes concentric when new. The expander ball does .004" of bending if used in the same step as when the brass is sized, but much less if the brass is already sized. The expander ball can be used later to bell the mouth of the case for cast bullets with little effect on concentricity. That is, if the expander ball is removed, the brass sized, the expander ball replaced, the case inserted into the die only far enough for the neck to be expanded but not sized, then the ball is not pulling when expanding, but pushing. The reason for the big difference between pushing and pulling with the expander ball is that pushing against a shell holder is more balanced than pulling. If the shell holder is open on one side, that side hangs back in pulling and the neck is bent toward that side. In forming 6mmPPC brass from 220Russian, a mandrel is used and never an expander. I did not under stand the difference and wrote professor Bradshaw [assistant professor back in 1994] [url=http://groups.google.com/group/rec.guns/browse_thread/thread/cb47be1a540f911e?hl=en&ie=UTF-8&q=Toby+Bradshaw+6mm+PPC+ball#b7facc7549be0ea5]Load development in a benchrest rifle - rec.guns | Google Groups[/url] The answer was pushing vs pulling. Here is Bart Bobbit telling me how he made his own concentricity gauge: [url=http://groups.google.com/group/rec.guns/browse_thread/thread/cab7ebc55b06c585?hl=en&q=mandrel+group:rec.guns+author:clark#9c65408c14e34ad3]Setting up a concentricity checker. - rec.guns | Google Groups[/url] [/QUOTE]
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