Went to town and picked up a box of .490" lead balls to measure some 45 Colt bores. I pounded 5 thru each of my Colts to get a good idea as what they are. The guns have 5 grooves, so measuring straight across with my mic doesn't give me the exact number I'm after since a land and a groove oppose each other. IIRC, I've read that most lands are .004" tall on S&W's. Is this a good way to get the proper measurement? Thanks in advance.
Help with measuring bore diameter please...
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Drive some through the chamber throats and measure them keeping track of which one they went through. Then use the chamber throats to measure the slug you drove through the bore. If your bore is slightly smaller than your throats your good.
Adding .004 would only work it your caliper had one jaw all the way in to the bottom of groove in bullet and the other 180 out.
Adding .004 would only work it your caliper had one jaw all the way in to the bottom of groove in bullet and the other 180 out.
OP
I think I have a local machine shop that has a set of pin gauges that I can measure my cylinder throats with. I do realize that my bore should be slightly smaller than the throats, but since there are an odd number of grooves, it's hard to get an accurate measurement of the bore diameter.
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Go to an auto parts store and get some shim material. Wrap it around the slug, measure, subtract shim thickness.
To measure that directly, you need a V anvil micrometer for 5 flutes. The flutes would normally be on a reamer or end mill cutting tool.
0.2-1" 108 Degree 5 Flutes Measured V-Anvil Micrometer
0.2-1" 108 Degree 5 Flutes Measured V-Anvil Micrometer
I have never worried about it to that point, but you could always fill one groove on the bore slug with a dab of epoxy putty, then when it has set use a fine file so its radius matches the ones on each side of it and measure it.
There is a small article in a Gun Digest from 19?? explaining how to measure odd land/groove bores.
Homer Powley (sp?) a Ballistics wizzard in the 60's/70's made the thing up I believe.
You need a V block of a certain angle ,,I think 120* but I'm just guessing now.
A micrometer and then using a math formula he made you put quantity you get from the mic reading in and Bob's your Uncle.
Homer Powley (sp?) a Ballistics wizzard in the 60's/70's made the thing up I believe.
You need a V block of a certain angle ,,I think 120* but I'm just guessing now.
A micrometer and then using a math formula he made you put quantity you get from the mic reading in and Bob's your Uncle.
Did a Google search for "how to measure odd land/groove gun barrel bores" and it came up with an article by By Wayne McLerran on Texas-mac.com web titled:
Measuring Groove Diameters of Odd Groove Bores
It has many suggestions, methods and diagrams including Homer S. Powley's method.
Measuring Groove Diameters of Odd Groove Bores
It has many suggestions, methods and diagrams including Homer S. Powley's method.
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That mic is: Shars 5 V micrometer 303-2346. If you buy one used, be sure it includes the standard to check zero.
I fooled around with a V-block and it was just too much trouble unless you have three hands.
I broke down and bought the micrometer above, and it's so much easier and consistent.
