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Old November 17, 2012, 12:23 AM   #1
SEHunter
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How do you read the RCBS Precision Mic?

I realize i am opening myself up to sounding like an idiot but i can not for the life of me figure out how to read this thing. There is no way it is giving an actual measurement. Based off what i see, my head space is 0.001? What the sam hill kind of measurement is that?

In the instructions, i understand what they say each line on each piece represents (i think) but what do the numbers represent? They make absolutely no sense to me. Why the heck is there a line below "0" on the body? Zero is zero! I will gladly accept an idiot joke if someone can help me make sense of this thing.
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Old November 17, 2012, 01:07 AM   #2
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Centerfire Central review and "how to" by Bill Wade.
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Old November 17, 2012, 01:08 AM   #3
tkglazie
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Here are the instructions
http://www.rcbs.com/downloads/instru...ecisionMic.pdf
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Old November 17, 2012, 05:23 AM   #4
HiBC
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The short answer,its a tool to make a comparative measurement.You are not trying to dimenionally check you fired brass to any dimension on a drawing.All you are trying to do is begiin with a number,any number,it can be .017.It does not matter.From that number you can determine how much you have set the shoulder back with your sizer die.Maybe you size it and it reads .019.That is a change of .002.That is what you need to know.

}The initial reading,.007,or .001 or .021,is simply to have a baseline to measure from.It is the change from pre-sized to post sized that the tool measures.

Its a good tool.Precision Shooting's Reloading Guide recomends them.Learn to use it and you will minimize case stretch.You will get maximum life for your brass.

If you are shooting a semi-auto,you will be able to control proper head clearance for safe,reliable lock up.

You are on a good track!!
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Old November 17, 2012, 08:46 AM   #5
SEHunter
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Ahh.. Thanks fellas.
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Old November 17, 2012, 10:45 PM   #6
jdillon
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HiBC is correct and the marking on the Precision Mic are relative and establish a baseline for setting up your dies. They are particularly useful for setting up dies on gas guns in which other headspace tools may not provide accurate measurements due to case distortion on extraction.
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Old November 18, 2012, 07:19 AM   #7
Bart B.
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SEHunter, I'm gonna get bold here, but I think RCBS included a set of instructions with that tool.
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Old November 18, 2012, 09:56 AM   #8
SEHunter
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lol, i know. I deserve that. Im an over analyzer. I read them 3 times but they never stated that the tool is for reference readings, not an exact measurement although i should have been able to come to that understanding on my own. Everey measuring tool i have used gives an exact measurement and i suppose thats what threw me off.

Regardless, now that i understand how to use it, i love it. Very excited to find out how proper head spacing with FL sizing will improve my results.
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Old November 18, 2012, 12:27 PM   #9
rox
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When using the Precision Mic to measure the case head-to-shoulder dimension the 'zero' mark on the thimble corresponds to SAAMI minimum chamber headspace dimension, e.g. 1.7867" for 6mm Remmington, 1.630" for .308 Win etc.

Although the tool is often used for relative measurements (e.g. setting the shoulder back 0.002") it is also useful for making absolute measurements, e.g. confirming that a case conforms to SAAMI dimensions or adjusting dies to achieve the same. The table in the instructions lists the chamber min/max dimensions for various calibers.

..
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Old November 18, 2012, 12:39 PM   #10
Bart B.
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SE, the instructions under the drawing of a 30-06 case referring to it explains it relative to the table of cartridge headspace dimensions.
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