Best way to measure diameter of barrel?

[thefitter]

Yes that's really the question. For some reason I'm having a hell of a time (in my mind) measuring the diameter of a barrel. I have good Mitutoyo digital calipers and digital micrometer. But I can't seem to find the proper placement so that I get a consistent reading. Trust me I don't usually have this problem, its embarrassing.

Thanks

 

[jwink]

Pin gauges are available in .0005 increments.

 

[Terry]

Outside diameter?

 

[thefitter]

Outside diameter?

Sorry, yes outside diameter.

 

[snakepit]

d=c/pi

d=diameter
c=circumference
pi=3.1417

My barrel is a 1.250" diameter barrel with a circumference of 3.93" (circumference measured with a string).

3.93" divided by 3.1417 = 1.250"

 

[Dusty Stevens]

Use the small points on your calipers?

 

['Freak]

What barrel contour is it and where along its length are you trying read outside diameter?

 

[dickn52]

What barrel contour is it and where along its length are you trying read outside diameter?

And there it is.

 

[hogpatrol]

Try a pi tape. :

 

[Dusty Stevens]

Id use an optical comparator, laser mic, or cmm

 

[thefitter]

What barrel contour is it and where along its length are you trying read outside diameter?

M14 profile, which has about a 6" straight section between the gas cylinder and the muzzle splines. Kreiger print says .585 but I can not verify.

 

['Freak]

What barrel contour is it and where along its length are you trying read outside diameter?

M14 profile, which has about a 6" straight section between the gas cylinder and the muzzle splines. Kreiger print says .585 but I can not verify.

A straight cylindrical section is measured from one side to the other or 180° opposite, same as if checking the outside diameter somewhere along the length of a bullet’s bearing surface, and complicated only if the area to be measured is inaccessible. … ... ?

 

[thefitter]

What barrel contour is it and where along its length are you trying read outside diameter?

M14 profile, which has about a 6" straight section between the gas cylinder and the muzzle splines. Kreiger print says .585 but I can not verify.

A straight cylindrical section is measured from one side to the other or 180° opposite, same as if checking the outside diameter somewhere along the length of a bullet’s bearing surface, and complicated only if the area to be measured is inaccessible. … ... ?

You are right thats why this is frustrating and I can not explain it. Using the tips of he calipers gets one reading. Moving up higher on the caliper flats gets another. Rotating the calipers around the barrel or laying them at an angle changes reading also. Micrometer readings fluctuate also. Tools have been checked with gauge blocks for accuracy and consistency.

I think I'm just going to call it a day, chaulk it up to dyslexia and say its .585 like the print reads.

 

[StevenDzupin]

It's Abbe error. The calipers are more accurate nearer the scale. :,not at the points.

 

[boiler_house7]

Maybe a ball mic with the taper on the barrel?