S
savage12LRPV
Guest
how do you measue a shot group? i would like to know the proper way so i can post up some from my savage 12 LRPV 
D
Dennis Sorensen
Guest
Center to center of the shots that are the farthest apart.
You can use calipers and measure from the outside of the holes and then subtract what one hole measures.
The holes usually do not measure exactly the same as the caliber.
You can use calipers and measure from the outside of the holes and then subtract what one hole measures.
The holes usually do not measure exactly the same as the caliber.
M
Montana Pete
Guest
When the holes are distinct on the paper, I have always measured the outside edge of the hole on one extreme with the inside edge of the hole on the other extreme. This gives you something concrete to measure from, rather than center to center, when you are trying to line up your caliper blade on air. I thought that the way I've described is the equivalent of center to center.
Of course, this would not work if you have all the holes blurred into one big hole.
If someone tells me I'm doing this wrong, I would not be offended, since I have much less experience than most of you.
Of course, this would not work if you have all the holes blurred into one big hole.
If someone tells me I'm doing this wrong, I would not be offended, since I have much less experience than most of you.
D
Dennis Sorensen
Guest
A device similar to this is normally used. It can be 'locked' on the target after acquiring the first hole and then adjusted to cover the other hole of the two farthest apart.
C
Cheechako
Guest
Montana Pete
There is nothing wrong with your method for groups where the individual holes can be discerned.
But there is no one method that fits all groups.
For the tiny dot Bencrest groups, outside to outside and subtract one bullet diameter.
For the average hunting rifle type group, your method works as well as any.
For BIG long-range groups, center to center if the groups are measured for competition purposes. If you're measuring BIG groups to determine the best load, then mean radius average is a much better test.
JMHO
Ray
There is nothing wrong with your method for groups where the individual holes can be discerned.
But there is no one method that fits all groups.
For the tiny dot Bencrest groups, outside to outside and subtract one bullet diameter.
For the average hunting rifle type group, your method works as well as any.
For BIG long-range groups, center to center if the groups are measured for competition purposes. If you're measuring BIG groups to determine the best load, then mean radius average is a much better test.
JMHO
Ray
A
abintx
Guest
I've found that the easiest method is to take a digital caliper, open it up to the diameter of your bullet (for instance .243), zero out your caliper, measure from outside to outside of the furthest spaced bullet holes ... and walla! ... you have your group size.
This will result on groups which measure 20-30thou SMALLER than actual size. In other words, a group which you measure at say .200 would come in at .230 or .240 for real.
al
To zero your calipers you should first shoot several single bullets into the paper and measure/zero on them.
Bullet holes never measure bullet diameter.
al
4
4Mesh
Guest
Fwiw,
looking at Dennis' photos, take a closer look at his photo showing the magnified bullet hole and his method for centering on that hole. There's actually two different methods used for determining where exactly the "Center" is. On short range targets, the "Grease Spot" is used, cause there's usually a very clean hole to deal with and the entire caliber is removed, (less the 10% or so mentioned multiple times above, which causes error).
Another method of centering on long range targets is to center a spot on the meplat hole. For bullets entering the target with significant wobble in flight, this can make a rather big difference in the group size that's measured, vs using the grease spot method. His example shows that grease spot method, using the black mark that's made to center up a circle on the optical magnifier. You can look closely and see also that his device would work for long range targets with still nice meplat holes also. His optic has a center spot as well. Using that on the Meplat hole is the other way. Either way, as long as your consistent is fine. I've seen though where as much as .030 of variation (and in some rare cases, even more) can be had by using the two different methods.
With good tools and a little experience, the measuring can be taken to quite a science.
Al, it's funny you mention about guys who can eyeball a group. Some are really tricky and the angles can really throw you off. Other times on easy groups more squared up to the target, I've called LR groups within .100 from 7' away and just glancing at it. I guess after ya done a few, it get's second nature. I remember joking around, in the target room (but serious too), calling close to center shots to be within x and y, spread of .005, and hit it on the mean! More than once... Had to get within 4 or 5' to do that tho...
looking at Dennis' photos, take a closer look at his photo showing the magnified bullet hole and his method for centering on that hole. There's actually two different methods used for determining where exactly the "Center" is. On short range targets, the "Grease Spot" is used, cause there's usually a very clean hole to deal with and the entire caliber is removed, (less the 10% or so mentioned multiple times above, which causes error).
Another method of centering on long range targets is to center a spot on the meplat hole. For bullets entering the target with significant wobble in flight, this can make a rather big difference in the group size that's measured, vs using the grease spot method. His example shows that grease spot method, using the black mark that's made to center up a circle on the optical magnifier. You can look closely and see also that his device would work for long range targets with still nice meplat holes also. His optic has a center spot as well. Using that on the Meplat hole is the other way. Either way, as long as your consistent is fine. I've seen though where as much as .030 of variation (and in some rare cases, even more) can be had by using the two different methods.
With good tools and a little experience, the measuring can be taken to quite a science.
Al, it's funny you mention about guys who can eyeball a group. Some are really tricky and the angles can really throw you off. Other times on easy groups more squared up to the target, I've called LR groups within .100 from 7' away and just glancing at it. I guess after ya done a few, it get's second nature. I remember joking around, in the target room (but serious too), calling close to center shots to be within x and y, spread of .005, and hit it on the mean! More than once... Had to get within 4 or 5' to do that tho...
W
wolf gray
Guest
Measuring groups
Dennis,
Do you just set the jewelers loupe on the plastic plate or have you got it glued on?
Thanks,
Dan Batko
"Where are we going and why am I in this basket?"
Dennis,
Do you just set the jewelers loupe on the plastic plate or have you got it glued on?
Thanks,
Dan Batko
"Where are we going and why am I in this basket?"
D
Dennis Sorensen
Guest
After I made the "aiming" circles (that took several attempts on scrap plastic first) I glued the loupe in place lightly with a plastic "glue" that melts the two together.
W
wolf gray
Guest
Measuring Groups
Dennis,
Thanks,
Dan
Dennis,
Thanks,
Dan
A
abintx
Guest
Al's got a very valid point. Push a bullet through a bullet hole and watch what happens. The paper opens up the the bullet diameter and then springs back on the edges to a smaller size hole. Measuring the smaller size holes, out size edge to outside edge, gives you a smaller group size.
To use Al's observations, and again for the sake of ease, take a digital caliper, open it up to the bullet diameter, subtract 30 thousandths, (we'll adjust on the conservative side, example: .243 minus .030 = .213), zero out your caliper, measure from outside to outside of the furthest bullet holes ... and walla again! ... you have your unofficial group size.
Got a scanner. Here's another way. And it's free.
http://www.ontargetshooting.com/
http://www.ontargetshooting.com/
C
Cheechako
Guest
I guess you can color me confused. This is on the General Discussion Forum and yet most answers seem to be directed at measuring the tiny Benchrest groups where precision in measurements can make the difference between winner and first loser.
For all other group measurements, including Long Range Benchrest, any variation of the center to center methods is good enough. I have measured and scored a lot of 1000 yard groups where all that was needed was a yardstick.
JMHO
Ray
For all other group measurements, including Long Range Benchrest, any variation of the center to center methods is good enough. I have measured and scored a lot of 1000 yard groups where all that was needed was a yardstick.
JMHO
Ray
D
Dennis Sorensen
Guest
Ray,
A group is a group regardless of size or distance shot...
The original question - how do you measue a shot group? i would like to know the proper way...
The proper way ( which does measure to the thousands of an inch) has been described as well as some variations of the center to center methods that are incorrect...
A group is a group regardless of size or distance shot...
The original question - how do you measue a shot group? i would like to know the proper way...
The proper way ( which does measure to the thousands of an inch) has been described as well as some variations of the center to center methods that are incorrect...
C
Cheechako
Guest
Dennis
My original post said that there was no one correct way to measure groups. It all depends on the particular situation. I still think that.
Center to center IS the most common but not always the best. Mean radius average is a much better method to judge the "quality" of large groups.
My point was that some groups do not need to be measured to the thousandths of an inch. Long range groups that may cover an entire target can be measured center to center to the nearest tenth or 1/8" and that is perfectly acceptable. I know of no precision measuring instrument that can measure a 48" group to the nearest thou. If you are measureing a group from grand-daddy's 30-30 you'd use a tape measure, most likely.
The Internet and Forums like BR Central have trapped many shooters into thinking that all rifles must shoot 1/4 MOA and that measureing groups to four decimals is the only way to judge accuracy potential. All that does in many cases is to take the fun out of shooting by setting unrealistic goals resulting in discouraged shooters.
JMHO
Ray
My original post said that there was no one correct way to measure groups. It all depends on the particular situation. I still think that.
Center to center IS the most common but not always the best. Mean radius average is a much better method to judge the "quality" of large groups.
My point was that some groups do not need to be measured to the thousandths of an inch. Long range groups that may cover an entire target can be measured center to center to the nearest tenth or 1/8" and that is perfectly acceptable. I know of no precision measuring instrument that can measure a 48" group to the nearest thou. If you are measureing a group from grand-daddy's 30-30 you'd use a tape measure, most likely.
The Internet and Forums like BR Central have trapped many shooters into thinking that all rifles must shoot 1/4 MOA and that measureing groups to four decimals is the only way to judge accuracy potential. All that does in many cases is to take the fun out of shooting by setting unrealistic goals resulting in discouraged shooters.
JMHO
Ray
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