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Rifles, Reloading, Optics, Equipment
Gunsmithing
Thoughts from the pro's
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<blockquote data-quote="Gcan" data-source="post: 1624661" data-attributes="member: 102867"><p>I think you may be missing one point. </p><p>Thread are often on a different axis than the bolt raceway. We don't datum off the threads. We use the raceway. We square the bolt bearing surfaces to the raceway. We machine the bolt lugs perpendicular to the bolt axis. We cut the bolt nose and face concentric and square. This makes the bolt, lugs and action bearing surfaces perfectly square. We face the action face and bolt bearing faces. Now everything is concentric.</p><p></p><p>At this point the threads are (never found a perfect one) either eccentric to the centerline axis of the bolt and action or angularly misaligned and also eccentric. So we cut the thread bore .010 (usually enough) oversize to get the thread bore concentric and recut the threads so everything is on the same axis. We end up with a 1.072-16 thread rather than the oem 1.062-16 thread. Chamber, Bolt, lugs, action centerline, face, barrel threads are as though it was all one piece of metal. </p><p></p><p>If you turned a old barrel blank straight and turned the tenon shoulder back. Then put the blank in a 4 jaw and screwed the action onto the blank until the face of the blank bottomed on the internal bolt bearing faces you could certainty square the action face to the thread axis but the action/bolt centerline would still not be concentric to the threads or barrel.</p></blockquote><p></p>
[QUOTE="Gcan, post: 1624661, member: 102867"] I think you may be missing one point. Thread are often on a different axis than the bolt raceway. We don’t datum off the threads. We use the raceway. We square the bolt bearing surfaces to the raceway. We machine the bolt lugs perpendicular to the bolt axis. We cut the bolt nose and face concentric and square. This makes the bolt, lugs and action bearing surfaces perfectly square. We face the action face and bolt bearing faces. Now everything is concentric. At this point the threads are (never found a perfect one) either eccentric to the centerline axis of the bolt and action or angularly misaligned and also eccentric. So we cut the thread bore .010 (usually enough) oversize to get the thread bore concentric and recut the threads so everything is on the same axis. We end up with a 1.072-16 thread rather than the oem 1.062-16 thread. Chamber, Bolt, lugs, action centerline, face, barrel threads are as though it was all one piece of metal. If you turned a old barrel blank straight and turned the tenon shoulder back. Then put the blank in a 4 jaw and screwed the action onto the blank until the face of the blank bottomed on the internal bolt bearing faces you could certainty square the action face to the thread axis but the action/bolt centerline would still not be concentric to the threads or barrel. [/QUOTE]
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Thoughts from the pro's
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