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measuring goups?

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Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: February/05/2008 at 22:54
ckk1106 View Drop Down
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how do you measure group size?  do you measure it from center of hole to the center of the furthest away hole?  Or do you measure from the outer edge to the outer edge of the furthest away hole?  Also when people say that their gun shoots sub moa, is that a 3 shot group?  I have been loading my 243 with RL19 44 gr, using hornaday 87 gr sp.  I have been shooting 5 shots at each spot on my target and usually get anywhere from 1.25 in to 2 inch measuring from the outermost edge of the holes.  I'm hoping that people measure from the center of each hole.   Thanks.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: February/06/2008 at 08:03
pyro6999 View Drop Down
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i dont know if this is the official way since i havent ever shot competitively but i always went outside edge to outside edge and then you subtract the diameter of your bullet, so in this case say the group was 1.25 and you shoot a .243win which shoots a .244bullet would give you a 1.006 almost a one inch group
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: February/06/2008 at 08:20
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how do you measure group size?
about everyway imaginable--competitor used to sell a plastic template that was really slick - it was an 8x10 clear plastic sheet with various circles rings on it for 2" 1" etc, and all you had to do was place the template over it and was a nice quick fix.
5 shot groups are nice
an aggregate type method of measurement is best, because it is possible to shoot 3-4 rds thru the same hole and 1 flyer and still get a small group, rather than a more statistical clover leaf type group
check also with 6mmbr web site.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: February/06/2008 at 09:33
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 The way I always did it for recordkeeping and load data purposes is like pyro said but using the jaws of a dial caliper laid flat on the paper, outside-to-outside and subtract one bullet diameter. This gives center to center dimensions with a good degree of accuracy. It's easy to figure because the measurements are expressed in thousandths of an inch and you don't need to do any conversions.
 As Dale mentioned, five or even ten-shot groups are more statistically relevant than  three, but it all depends on what you're going to do with the data anyway as to how important that is.
 Multi-group aggregates are more useful yet. (And often less impressive to your buddies than a hand-picked good 'un.)
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: February/06/2008 at 09:52
ckk1106 View Drop Down
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Is the .243 considered an accurate round?  I have a Cartridges of the  World book, and the editor says that this caliber has a history of errant performance, whatever that means.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: February/06/2008 at 09:59
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it can be for sure, my dads .243 is one of the best shooting rifles i have ever loaded for, its based on the .308 case so its inherently accurate due to that, its just finding the perfect combo to make it that way, my dads is an m70 with a bullbarrel so its not a recoiling rifle which helps the accuracy alot, errant, eratic not, consistant, etc
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: February/06/2008 at 10:23
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In general, the method described is correct -- for a "quick and dirty" measurement.  You want to measure the center to center distance of the two bullet holes at the widest portion of the group.  This method -- measuring the widest point and subtracting one bullet diameter -- gives you a close approximation that serves your purposes for expressing hunting load accuracy.

However, keep in mind the actual bullet hole size in the paper is usually smaller than the actual bullet diameter (the amount depending on the type of paper) because the paper bends and stretches some as the bullet passes through it.  So, if you want to measure groups by competition standards, you have to be more precise than the method above, which always gives a group size number that's smaller than it actually is.
 
This describes the "official" method:


Edited by RifleDude - February/06/2008 at 10:40
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: February/06/2008 at 10:30
pyro6999 View Drop Down
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nice find ted thanks!! i have wondered if i was doing it right or if it was just wonky made up thing i came up with!
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