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Discussion Starter #1
I'm looking for a high quality digital caliper for measuring bullets. My searchs on the Inet have turned up some nice models at reasonable prices, but they all only have accuracy to .001. From what I have read about reloading it appears as this is not sufficient. Am I wrong? Is .001 really enough precision?
 

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.001 is enough for me. No reloading manuals I have seen go more accurate than .001". I doubt you will notice any more accuracy or consistancy by going any more obsessive/compulsive than .001", especially in a handgun.
 

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For measuring bullets, I prefer a micrometer, accurate to .0001, but .001 is probably close enough for handloading purposes.
 

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A caliper capable of accuracy to 0.001 in should be good enough for re-loading, since most dimensions given for re-loading are to the 3rd decimal only.
 

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Any mathematicians here? It seems to me that, if you don't have your caliper precisely perpendicular to the axis of your bullet, you won't get an absolutely true reading on bullet diameter. So the question is, how large an error is created by what degree of cant in the caliper/bullet orientation? Is that error great enough to make a tool with .0001 precision superfluous?

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Discussion Starter #6
Originally posted by jpwright:
Any mathematicians here? It seems to me that, if you don't have your caliper precisely perpendicular to the axis of your bullet, you won't get an absolutely true reading on bullet diameter. So the question is, how large an error is created by what degree of cant in the caliper/bullet orientation? Is that error great enough to make a tool with .0001 precision superfluous?


I just ordered a nice digital model from PennToolCo.com. Accurate to .0008 , only cost $49.95 (model #PYT-202).

I do have a background in math and chemistry. If you want to measure accurately to .001, you need an instrument with a degree of precision at least 1/2 of 1 decimal point more to the right, hence for .001 accuracy you would want the degree of error to be no more than .0005. Unfortunately, that extra .0003 more than doubles the price of the instrument, at least in the searches I have done.

With regard to being off axis when measuring OAL, the simplest solution is to take 3 measurements, removing the bullet from the tool and then reinserting it. This should resolve any off axis problems. If the measurements are way off either your caliper has problems or you do.

regards,

gary
 

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Gary,

A caliper, whether vernier, dial, or digital, reading to 0.001" is useful and adequate to measure OAL/seating depth, and case length before and after trimming. Use the depth gauge to measure the protrusion of the stem of the seating die at a given OAL and simplify getting back to a previous load even if you don't have an expensive micrometer seating die in that caliber.

However, to measure bullet diameters for matching to barrel specs, to slug the barrel and get its specs to begin with, and to measure casehead expansion at maximum (rifle) loads, you need a micrometer, preferably a 0.0001" model. Pistol bullet diameter can matter in .0005" increments, rifle less still. I mean a Starett or Mitutoyo for about a hundred bucks. Plan on paying more for direct reading, more still for electronic. A Mitutoyo Digimatic is $136 from Brownells. I got my Starrett 1"X.0001" at a pawn shop for $40, but I had my gunsmith looking over my shoulder and ok'ing the deal. There are a lot of worn out tools out of pawn.

You don't need a micrometer to load pistol ammo from store-bought components. I had a batch of those coated Precision bullets somebody touted that measured only .450" instead of the .452" that a lead .45ACP should be. That error showed on calipers.
 

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We've been tossing the "digital" question about on www.accuratereloading.com.

In a digital model you have a point between two numbers where the instrument stops indcating one integer and moves to the next integer . . . goes from "3" to "4" . . .

OK, where's that shift point? Digital scales are accurate to 0.01 gr. At what point does the scale move from 0.1 to 0.2? Is it 0.14, 0.15, 0.16, 0.17 . . . ???

With a mechanical caliper, it's possible to view the range between the integers on the dial. Also, you calibrate the instrument by aligning the witness mark on the dial with the needle/hand on the dial. I "calibrate" my caliper every time I use it. Dander, grease, lint, and everything else will cause the jaws of a caliper to vary in its reading. I wipe the jaws and check the dial every time I use it. You can't do this with a digital instrument.

Back to the scale . . . I weigh bullets and brass for bench loading with a digital scale. It's fast. I don't need to move a poise along a beam to weigh each individual item.

BUT . . . when weighing charges for bench rest/varmint loads, I use a beam scale where I can determine precisely where the beam falls between the witness marks on the dial. So while the beam scale is calibrated to 0.1 gr. just like the digital . . . I can "read" the scale probably out to 0.01 gr. or thereabouts -- not precisely, but more accurately than a digital with accuracy to 0.1.


Same principle applies to a digital caliper.

Measure several times. Most ammo has "runout" -- it's not concentric, and will vary in diameter. OAL in most ammo varies depending where you measure from base to tip of the bullet. The base is not uniformly flat.

Bench shooters sit up nights worrying about this stuff. Sinclair Precision Reloading addresses these concerns.
http://www.sinclairintl.com/

[This message has been edited by Genghis (edited 11-22-2001).]
 

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Discussion Starter #9
AS long as the digital caliper displays more decimal points than you need precision wise you don't need to worry about 'when it turns'. Example, if you are measuring OAL and you want accurate reading to 3 decimal places (1.123) you need to make sure the caliper reads to 4 decimal places( 1.1234). This gives you the level of precision you need.

gary

Originally posted by Genghis:
We've been tossing the "digital" question about on www.accuratereloading.com.

In a digital model you have a point between two numbers where the instrument stops indcating one integer and moves to the next integer . . . goes from "3" to "4" . . .

OK, where's that shift point? Digital scales are accurate to 0.01 gr. At what point does the scale move from 0.1 to 0.2? Is it 0.14, 0.15, 0.16, 0.17 . . . ???

With a mechanical caliper, it's possible to view the range between the integers on the dial. Also, you calibrate the instrument by aligning the witness mark on the dial with the needle/hand on the dial. I "calibrate" my caliper every time I use it. Dander, grease, lint, and everything else will cause the jaws of a caliper to vary in its reading. I wipe the jaws and check the dial every time I use it. You can't do this with a digital instrument.

Back to the scale . . . I weigh bullets and brass for bench loading with a digital scale. It's fast. I don't need to move a poise along a beam to weigh each individual item.

BUT . . . when weighing charges for bench rest/varmint loads, I use a beam scale where I can determine precisely where the beam falls between the witness marks on the dial. So while the beam scale is calibrated to 0.1 gr. just like the digital . . . I can "read" the scale probably out to 0.01 gr. or thereabouts -- not precisely, but more accurately than a digital with accuracy to 0.1.


Same principle applies to a digital caliper.

Measure several times. Most ammo has "runout" -- it's not concentric, and will vary in diameter. OAL in most ammo varies depending where you measure from base to tip of the bullet. The base is not uniformly flat.

Bench shooters sit up nights worrying about this stuff. Sinclair Precision Reloading addresses these concerns.
http://www.sinclairintl.com/

[This message has been edited by Genghis (edited 11-22-2001).]
 
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