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Rifles, Reloading, Optics, Equipment
Gunsmithing
Why dial a rifle bore within .0001"
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<blockquote data-quote="Canadian Bushman" data-source="post: 1141814" data-attributes="member: 41122"><p>Of course the feature being measured dictates much of the attainable accuracy of measurments. </p><p></p><p>However even with a C.M.M. I doubt the runout of a rifle bore could be accurately measured within tenths. My company owns 3 zeiss C.M.M.'s. Each one cost close to $1m. They are resting on 2 ton granite slabs ground to .0002" flatness ( if youve never seen the guys lap these things in every 6mo its something to watch.) </p><p></p><p>Majority of the time these three machines wont agree within .0003", and on parts wayyyyy easier to measure than a rifle bore. As accurate as they are, you still gotta know when to trust them and when to question them. </p><p></p><p>Consider this. If you are using a grizzly rod 12" in length, and measuring in the middle, your indicator is only moving half of what the tip of the rod is moving. Assuming there isnt any slop in the bushings and assuming its actually following the bore exactly. </p><p></p><p>You ever roll one of those things across a surface plate?</p><p>Ever check the alignment of the jacobs chuck holding the far end? </p><p></p><p>Im not saying we shouldnt all try to get rifles bores dialed as close as possible. Thats a given. Im just saying ive never gotten any significant length of a rifle bore to run inside .0001" ( on a grizzly rod ), and ive never told a customer i did.</p></blockquote><p></p>
[QUOTE="Canadian Bushman, post: 1141814, member: 41122"] Of course the feature being measured dictates much of the attainable accuracy of measurments. However even with a C.M.M. I doubt the runout of a rifle bore could be accurately measured within tenths. My company owns 3 zeiss C.M.M.'s. Each one cost close to $1m. They are resting on 2 ton granite slabs ground to .0002" flatness ( if youve never seen the guys lap these things in every 6mo its something to watch.) Majority of the time these three machines wont agree within .0003", and on parts wayyyyy easier to measure than a rifle bore. As accurate as they are, you still gotta know when to trust them and when to question them. Consider this. If you are using a grizzly rod 12" in length, and measuring in the middle, your indicator is only moving half of what the tip of the rod is moving. Assuming there isnt any slop in the bushings and assuming its actually following the bore exactly. You ever roll one of those things across a surface plate? Ever check the alignment of the jacobs chuck holding the far end? Im not saying we shouldnt all try to get rifles bores dialed as close as possible. Thats a given. Im just saying ive never gotten any significant length of a rifle bore to run inside .0001" ( on a grizzly rod ), and ive never told a customer i did. [/QUOTE]
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Rifles, Reloading, Optics, Equipment
Gunsmithing
Why dial a rifle bore within .0001"
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