Using a Micrometer

**ah141nj** · February 17th, 2009, 10:12 PM

Hello All,

Stupid question. How are you supposed to accurately measure a case wall with a micrometer? The case wall is round while the anvils on the micrometer are flat. Is there a trick I need to know about?
Looking to measure the wall thickness for an accurate crimp.

Crimp = 2x brass thickness + bullet diameter

I thought a micrometer was better to use than a caliper.

**H.E. Pennypacker** · February 17th, 2009, 10:17 PM

Originally Posted by ah141nj

Hello All,

Stupid question. How are you supposed to accurately measure a case wall with a micrometer? The case wall is round while the anvils on the micrometer are flat. Is there a trick I need to know about?
Looking to measure the wall thickness for an accurate crimp.

Crimp = 2x brass thickness + bullet diameter

I thought a micrometer was better to use than a caliper.

You need a micrometer with a rounded top.

http://cgi.ebay.com/STARRETT-OUTSIDE-MICROMETER-211XP-ROUND-ANVIL-UNUSED!!_W0QQitemZ230302643085QQcmdZViewItem

http://www.mytoolstore.com/starrett/micro017.html

http://www.mytoolstore.com/starrett/micro021.html

The second link is probably the only one that would work in such a small space.

**SteveWag** · February 17th, 2009, 10:20 PM

If you want to measure a case wall, or the wall thickness of a tube, you need to use a tube micrometer. The tube micrometer has a round ball for the fixed anvil. The diameter of the anvil needs to be smaller than the ID of the tube.

Steve

**H.E. Pennypacker** · February 17th, 2009, 10:33 PM

So the top is called the 'anvil,' ey...

Been using micrometers for years and never knew that. Thanks.

**Kaos** · February 17th, 2009, 10:35 PM

Originally Posted by SteveWag

If you want to measure a case wall, or the wall thickness of a tube, you need to use a tube micrometer. The tube micrometer has a round ball for the fixed anvil. The diameter of the anvil needs to be smaller than the ID of the tube.

Steve

Couldn't you use a caliper as well?

**jsc83** · February 18th, 2009, 01:11 AM

Sorry, I don't know the technical terms, but the pointy end of the micrometer is for measuring inside dimensions. Can't you get the case thickness by taking the overall outside dimension minus the inside dimension and divide by 2? That would avoid having to buy additional tools.

**P-11 shooter** · February 18th, 2009, 01:15 AM

I have a micrometer and a dial caliper.

Both measure down to a thousanth of an inch. I say get a good caliper. Digital is nice too.

**Warpt762x39** · February 18th, 2009, 01:19 AM

Originally Posted by Kaos

Couldn't you use a caliper as well?

Micrometers are more accurate and usually measure in smaller increments.

**P-11 shooter** · February 18th, 2009, 01:42 AM

Originally Posted by Warpt762x39

Micrometers are more accurate and usually measure in smaller increments.

Generally, yeah. But a good digital caliper will measure to .5 thousandths while being faster to use, more versatile, give you a bigger range of measurement, and much easier to read.

P-11goodenoughforthegirlsIgowithSHOOTER

**Warpt762x39** · February 18th, 2009, 01:51 AM

Originally Posted by P-11 shooter

Generally, yeah. But a good digital caliper will measure to .5 thousandths while being faster to use, more versatile, give you a bigger range of measurement, and much easier to read.

P-11goodenoughforthegirlsIgowithSHOOTER

With something as thin as a case neck, I would want to measure to .001". Not .005". Thats just me but I grew up with a lathe in the garage and a dad who worked making jet engine parts. I'm used to measuring things a little smaller than most people like down into the .0001".

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