Measuring diameter with odd grooves

[Jtarm]

I know I saw a post somewhere on measuring groove diameter in barrels with an odd number of grooves (like S&Ws).

Could someone kindly point to it?

[tazman]

http://castboolits.gunloads.com/google.php?cx=partner-pub-6216953551359885%3A1942134700&cof=FORID%3A9&ie=ISO-8859-1&q=measuring+barrel+slug&sa.x=0&sa.y=0&siteurl=castboolits.gunloads.com%2Fshowthread.php% 3F381914-Measuring-diameter-with-odd-grooves&ref=castboolits.gunloads.com%2Fforumdisplay.php%3F 8-Cast-Boolits&ss=14457j16494987j25

The link is to a search result that gives links to several threads on the topic.

[Rizzo]

I know I saw a post somewhere on measuring groove diameter in barrels with an odd number of grooves (like S&Ws).

Could someone kindly point to it?

No link to it but what I did was to tightly wrap a .001" feeler gauge around the lead "slug" and measured it with a micrometer.
Then subtract .002" from your measurement to get your actual groove diameter.
Do it a few times to check for consistency.

[DougGuy]

In lieu of a mathematical value to assign to a slug, try this simple test. Push a soft lead ball through the bore, then see if it will go into the cylinder throats from the front. If it does, then the throat to bore relationship is likely correct.

It doesn't really tell you any decimal figures, it tells you that the throats are larger than groove diameter, and if you size the boolit to fit the throat, the boolit will be of sufficient diameter to seal in the bore and likely shoot well.

This is the poor man's cylinder mic if you will..

[pastera]

Have access to a 3d printer?
If so, I created a model for a 108° (5 groove) v-block adapters for both a micrometer and calipers that you can print.

http://castboolits.gunloads.com/showthread.php?189557-Measuring-a-5-groove-slug/page2

[tazman]

In lieu of a mathematical value to assign to a slug, try this simple test. Push a soft lead ball through the bore, then see if it will go into the cylinder throats from the front. If it does, then the throat to bore relationship is likely correct.

It doesn't really tell you any decimal figures, it tells you that the throats are larger than groove diameter, and if you size the boolit to fit the throat, the boolit will be of sufficient diameter to seal in the bore and likely shoot well.

This is the poor man's cylinder mic if you will..

This^^^^^ is what I do to check barrel dimensions. I also see what diameter boolits will fit through the cylinder throats.

[Jtarm]

In lieu of a mathematical value to assign to a slug, try this simple test. Push a soft lead ball through the bore, then see if it will go into the cylinder throats from the front. If it does, then the throat to bore relationship is likely correct.

It doesn't really tell you any decimal figures, it tells you that the throats are larger than groove diameter, and if you size the boolit to fit the throat, the boolit will be of sufficient diameter to seal in the bore and likely shoot well.

This is the poor man's cylinder mic if you will..

It’s on its way to ya Doug. It won’t go through.