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Re: Groove diameter
Posted by Wayne McLerran on Thursday, 14 August 2014, at 12:36 a.m., in response to Re: Groove diameter, posted by Wayne McLerran on Wednesday, 13 August 2014, at 11:47 p.m.
Oops, ignore my earlier measurements. I screwed up and transposed the measured values, but the point I made is still valid. Following are the corrected data and comments:
I beg to differ. You can get close but measuring across the corners may be off around 0.002" to 0.003". To verify I just measure the groove diameters of two Cerrosafe chamber casts made from the same TD carbine. Measuring across the corners with a high-quality vernier caliper and a standard micrometer the average was 0.4636". The V-anvil micrometer measured 0.4611". The differences may be because, although close, the width of the lands and grooves in my carbine are not exactly equal
Now, to determine the land heights (also called groove depth), measure across one land and the opposite groove with a standard micrometer or vernier caliper, then subtract the value from the V-anvil measurement. Therefore 0.4611" - 0.4557" = 0.0054", which is the height of one land. Finally, to determine the bore (land) diameter subtract 2X the land height from the groove diameter, i.e. 0.4611" - 2(0.0054") = 0.4503". So my TD carbine has a groove diameter of 0.4611" and a bore (Land) diameter of 0.4503".
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