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measuring cases to .0001

 
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  #8  
Old 04-01-2012, 12:22 PM
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Re: measuring cases to .0001

Quote:
Originally Posted by rscott5028 View Post
You could set up a dial indicator similar to the Sinclair bullet sorting stand, but with a Hornady or similar headspace insert.

If you are that anal, you will likely need to shave the case heads square on virgin brass with a Wilson case trimer turned backwards. (a very delicate procedure that can be unsafe if done incorrectly) Then fireform, verify TIR to a similar degree of precision, discard 90% of your premium Lapua brass, resize, and then measure.

All this assumes your chamber and boltface are perfectly square.

Otherwise, the case head doesn't allow for a precise index point with that level of precision.

-- richard
The long travel dial indicators are really not all that accurate, but if you gotta use one then use one with a digital read out (gets rid of the backlash from the gear & rack). The nest issue with those long travel indicators is that they have to have the setup fairly well centered because they don't handle a side load well. If the indicator has a bar or something like that attached to the stem it will not work as well. I built one once that used the digital scale similar to the ones used on a Bridgeport Z axis. The ram was attached to the scale, and I made some little adapters that went in the ram to seat on the datum line. It was good for .0005" consistently. I had a case that I called the master for each caliber I measured, and I used it to set the zero point on the scale. Wasn't perfect, but better than using calipers. The whole thing was very simple, and the only hard thing was mounting te scale and reader head.

gary
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  #9  
Old 04-01-2012, 12:45 PM
Edd Edd is offline
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Re: measuring cases to .0001

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Originally Posted by Whopper Stopper View Post
Do any calipers measure to .0001?

If so which ones and if not, what tool do you use when wanting a ten thousandths measurement on case shoulder lengths where a micrometer is too short? I want to set bump die and want to know exactly where it is at.

Thanks for any replies much appreciated.

WS
The graduations are wide enough on a standard dial caliper to split a .001" in a couple of segments if that is important to you.

If you think you can size case lengths to a tolerance of .0001" you are a dreamer. I'd wager that in a blind test you can't repeatedly measure the same case to a .0001".
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  #10  
Old 04-01-2012, 01:00 PM
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Re: measuring cases to .0001

Diito,And as noticed on here,speed you use amount of lube and other factors add to different #'s.Redding has a die type,mouted inyour press dial indicator,but good to .001. $120 ANDI dont see a advantage to it over caliper w/insert, which is fast and handy.

Last edited by sp6x6; 04-01-2012 at 02:14 PM.
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  #11  
Old 04-01-2012, 01:09 PM
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Re: measuring cases to .0001

Quote:
Originally Posted by Trickymissfit View Post
The long travel dial indicators are really not all that accurate, but if you gotta use one then use one with a digital read out (gets rid of the backlash from the gear & rack). The nest issue with those long travel indicators is that they have to have the setup fairly well centered because they don't handle a side load well. If the indicator has a bar or something like that attached to the stem it will not work as well. I built one once that used the digital scale similar to the ones used on a Bridgeport Z axis. The ram was attached to the scale, and I made some little adapters that went in the ram to seat on the datum line. It was good for .0005" consistently. I had a case that I called the master for each caliber I measured, and I used it to set the zero point on the scale. Wasn't perfect, but better than using calipers. The whole thing was very simple, and the only hard thing was mounting te scale and reader head.

gary
Gary,

I consider you the master of working with close tolerances. So, I wouldn't knowingly disagree with anything you stated on the subject.

I would simply ask the question as to how you would consistently take such a precise measurement as requested by the OP (.0001") if you aren't certain that your case head is square to the body to at least the same degree of precision?

Most digital calipers will give a reading to the nearest .0005". I have no idea how trustworthy that reading is. But as a relative comparison, spinning the case will cause the reading to fluctuate which I suspect is a function of (a) pressure/technique, and (b) case heads that are slightly out of square.

i.e. ye olde banana case theory

-- richard
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  #12  
Old 04-01-2012, 03:26 PM
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Re: measuring cases to .0001

Now, if it was me (not that I need that accuracy as 0.001 is fine), I'd set up my digital height master on the surface plate and set the height master to the required dimension with my Weber Cro-Blocks and then gage the cases to the set standard.

Cro-Blocks are good to 0.000001 give or take, depending on ambient temperature.

.....keep in mind that production chambers are typically a couple thousands tolerance......
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  #13  
Old 04-01-2012, 03:27 PM
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Re: measuring cases to .0001

calipers won't work because they use inconsistent pressure and are only good for a few thou anyway. You can use a mic but your trying to measure a non square case mouth on one end and a stamped base on the other.
There isn't an inspector around that uses either a mic or calipers for .0001 which is +-.00005. Then there is the ambient temperature thing....
After that, the rest of your gear isn't close to .0001.
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  #14  
Old 04-01-2012, 03:35 PM
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Re: measuring cases to .0001

"I want to set bump die and want to know exactly where it is at."

You may think you're serious but getting more than one shoulder set back consistant to a tenth is not in the range of reality nor would it make any difference down range if it were; this stuff just isn't that repeatable. (But you will soon realize that as soon as you start trying to measure it.)

Good luck!
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