Practical Ballistics by Lewis Potter

Author:Lewis Potter
Language: eng
Format: epub
ISBN: 9781847977380
Publisher: The Crowood Press

Checking Concentricity

For checking concentricity, a dial indicator mounted on its own right-angled precision base, or with a magnetic base on a surface table, will suffice. Most industrial dial indicators measure down to 0.001in (one thousandth of an inch),some to 0.0005in (half a thousandth of an inch), and the latter, if one can be found, is preferable.

The simplest way of checking is to mark the bullet in four equally spaced places, then roll it under the dial indicator in the first position to be checked, and set it at zero. When rolling it under in the other three positions, if the dial indicator reads other than zero, this shows some eccentricity or ovality of the bullet. This is not confined to cast bullets, and it can be an interesting exercise to check jacketed ones just to compare makes.

Another method which is a bit fiddly but is possible with really large calibre bullets is to rotate the bullet in a V block mounted directly under the dial indicator. With large bullets it is not a problem, but small bullets and short fingers can make it an impossible task to get anything like consistent results.

The other aspect of concentricity does not directly concern the bullet, but how it is held in the cartridge case.

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