Question About "Group Size"

Discussion in 'Rifles, Bullets, Barrels & Ballistics' started by jhendri2, Apr 17, 2002.

  1. jhendri2

    jhendri2 Well-Known Member

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    Oct 25, 2001
    Actually you measure the size of the hole and subtract the bullet diameter, e.g. if the hole measures .408 and you are shooting and you are shooting a 308 caliber rifle your group size would be .100 (.408{hole}-.308{caliber}=.100{group size}).

    My smallest 5 shot group to date is .172 shot with a 308 win at 100 meters. The actual "hole" was .480.

    Hope this helps.

    Jim

    [ 04-17-2002: Message edited by: 338Lapua ]
     
  2. Dave King

    Dave King Well-Known Member

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    EDITED: Looks like you got two answers at the same time.


    If I understand what you're asking then this is the answer.

    If I shoot a .243 bullet through a target and then measure the hole it should be .243 (+-). I then measure the distance across this same hole and subtract one caliber diameter and that's the group size .243 - .243 = 0 (no one shot groups are ever anything but 0 in size).

    If I have a .308 caliber that shoots to one ragged hole with 3 or 5 shots, I also then measure across the hole and subtract .308. If the hole is .355 across and the caliber is .308 the group is .047 (.355 - .308 = .047).

    What were doing in measuring these groups is determining the distance from the exact center of the first hole that the furthest bullets' exact center deviated.

    Don't think of the entire hole of the first shot (hole), think only of the exact center of this hole, an infinitely small speck in the exact center.

    Remember, a one shot group has 0 deviation and therefore it's a group of 0 size.

    [ 04-17-2002: Message edited by: Dave King ]
     

  3. Jim Bergmann

    Jim Bergmann Member

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    Okay, I think I have it. So in a group which has paper between the holes (i.e., not "one ragged hole"), you measure the two holes farthest apart, and still then subtract out the bullet diameter?

    Thanks, and I appreciate your patience and explanations!
     
  4. Steve Shelp

    Steve Shelp Well-Known Member

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    Jim,
    It doesn't matter if the bullets are touching or not. You simply measure outside to outside of the 2 farthest shots and subtract your caliber size. They could be overlapping by 90% or 3" between the shots, the same method applies. This will give you the center-to-center measure of any 2 bullet holes in a target. Now when they truely cut a ragged hole like the BR guys do it's really hard to tell where the 2 farthest edges are, so optical lenses and special measring devices are used in competition. And even then it's not an exact science.

    Also one other note: the black ring left in a target measures smaller then the actual bullet diameter. For instance if you measure a .243 caliber bullet hole it will probably measure about .228 +-. But this is really splitting hairs and only comes into play when trying to determine a BR reocrd or something. When it comes to measureing my test groups at home and stuff I keep it simple and subtract the actual bore diameter rather than measurering what size hole my bullet produces in a particualr type of paper target, what type of backer it has, etc.

    Hope this helps,
    Steve

    [ 04-17-2002: Message edited by: Steve Shelp ]
     
  5. Jim Bergmann

    Jim Bergmann Member

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    Feb 20, 2002
    Hi Guys:

    I have been a hunter for a long time, but would like to develop into a "shooter" as well. I am about to get into handloading, and will work to develop and improve my shooting skills. To that end, I have devouring the seemingly endless amount of quality experienced-based information on this and several other forums.

    Anyway, on to what my question relates to. I have read many different posts from people concerning loads and what have you, and they typically mention and specify group size. However, some of these groups are not only impressive, but downright extraordinary, and in my opinion, maybe nearly physically impossible. Now correct me if I'm wrong, but group (of 2 or more shots) size is measured from center to center of the two shots farthest apart, right? Or if the group is only one hole, from one side of it to the other. And theoretically, a "group" of one shot could certainly be no smaller than the diameter of the bullet (obviously), and in fact, would realy be a little larger, because it would punch an opening through paper that would be somewhat larger than the bullet, right?

    So, tell me then how can someone shoot a .24 inch group with a .243, or a .3 inch group with a .308 or other 30 caliber rifle? Maybe I'm missing something here, or maybe folks aren't extremely precise w/their measuring, or maybe they exaggerate a little?

    If anyone has a comment or an explanation, please go for it. Thanks... [​IMG]