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