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I’m puzzled, just how is a bullet group measured. Is it center to center or inside edge to inside edge or possibly outside edge

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  • I’m puzzled, just how is a bullet group measured. Is it center to center or inside edge to inside edge or possibly outside edge

    I’m puzzled, just how is a bullet group measured. Is it center to center or inside edge to inside edge or possibly outside edge to outside edge? In fact, the last one was the one I thought was used, because people have made comments like you could cover the group with a dime, implying a measurement of outside edge to outside edge. In the past I never gave it a lot of thought. What brings me this great puzzlement is an article I read on the eye-popping .178 inch group made by a .30 caliber rifle What puzzled me was how do you get a group almost half the diameter of the .30 caliber bullet used. The way I see it, if the bullet is a .30 caliber, and each one of a group went straight through the same whole each time wouldn’t it be a .30 inch group? Wouldn’t you have to have bullets at least as small as the .178 inch group measurement to have a group that size? Also how do you measure a ragged edge hole in paper made by a spinning bullet down to a thousandth of an inch. I mean that’s almost as thin as the whiskers on the chin of a gnat. Ragged edged holes? Maybe a hundredth of an inch, maybe, but a thousandth? Do you go with the inside edge of the ragged edge or the outside edge of the ragged edge? It seems to me the raggedness of it is more then a thousandth of an inch. Is there a chance some one on your staff could answer these questions? Alan Duhon Newport News, Va

  • #2
    Scoring is based on outside edge of hole.

    Group size is center to center distance between the widest two holes in the group. For practical non-competitive situations, just guess at the centers. If you can't determine the centers then measure the largest outside to outside distance in the group, and subtract the bullet caliber (convert to inches). Subtracting the bullet diameter is the same as subtracting the radius (center to edge) of the two bullet holes, giving center to center distance.

    The hole itself might be bigger or smaller than the bullet diameter. If that is the case I look for the dark imprint the bullet left in the paper and use the outside edge of the imprint.




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