I have been shooting just over a year. I see publicatios that show a one inch shot group in a couple of ways. They are scattered or in a cluster. Sometimes inside a 3in radius or 5in radius target. I put 20 0f 25 shots in a 3in radius. So am I shooting a 3 in group? If not, what are the standards to gauge ones shot group.
What and how to measure a shot group
- Thread starter bulldog1
- Start date
Sounds about right olmoss
The other way is to measure from the left side of the left most hole & the left side of the rightmost hole.... then from the top of the topmost hole, to the top of the bottom most hole.... just read the measurements
Saves having to subtract the caliber (especially if you flunked kindrgarten like I did)
The other way is to measure from the left side of the left most hole & the left side of the rightmost hole.... then from the top of the topmost hole, to the top of the bottom most hole.... just read the measurements
Saves having to subtract the caliber (especially if you flunked kindrgarten like I did)
Typical group measurement is center-to-center of the two holes farthest apart in the group.
That's if someone is talking about group sizes. There are other ways to measure accuracy, but usually there will be some pretty obvious hints that they're not simple group size measurements.
That's if someone is talking about group sizes. There are other ways to measure accuracy, but usually there will be some pretty obvious hints that they're not simple group size measurements.
Going back to your original example, "20 0f 25 shots in a 3in radius", it's reasonable, especially when the number of shots in a group is quite large, to throw out a few shots if you "called" them as being bad shots.
Calling a shot bad means that when the shot broke you said to yourself: "That shot was high and left." It doesn't mean you shoot a bunch of shots, go down to look at the group and say to yourself: "If I throw these two shots out my group size goes down by half."
Calling a shot bad means that when the shot broke you said to yourself: "That shot was high and left." It doesn't mean you shoot a bunch of shots, go down to look at the group and say to yourself: "If I throw these two shots out my group size goes down by half."
inSight-NEO
New member
Im sure Im wrong here, but I think of a circle (with the first shot being the centerpoint) and all following shots as "endpoints" which then connect back to the first "centerpoint" shot (ie., forming a radius). From there, I calculate a basic shot group in inches.
I tend to take the best 3 shots (within a group) when considering the potential accuracy of a weapon.
I tend to take the best 3 shots (within a group) when considering the potential accuracy of a weapon.
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Note how most people are giving you diameters (measuring the two holes farthest apart). Perhaps those stating a radius are just mis-speaking. But a 3 inch radius is a 6 inch diameter for the same circle.
So I propose always dividing your diameters by two and reporting radiuses! To those who hear "diameter" in their mind you'll seem twice as accurate.
So I propose always dividing your diameters by two and reporting radiuses! To those who hear "diameter" in their mind you'll seem twice as accurate.
There are a number of problems with the traditional way of evaluating firearm accuracy (it's really precision - accuracy is achieved by adjusting the sights) using the "group size" method. (I recognize this thread is in the handgun section, but group size analysis is really something that is done more seriously with rifles, even though the same procedures work for either.)
The first is that, no matter how large your group, you're essentially only using the information provided by the two shots that fall farthest apart. There's much more information available if you can somehow factor in what the other shots are telling you.
Second, the group size is unavoidably linked to the number of shots you fire - on average, 3-shot groups from the same gun must be smaller than 5-shot groups, which must be smaller than 10-shot groups, etc. Related to that is the fact that the group can never get smaller as you add shots to it, only larger. There's something inherently unsatisfying about that.
Third, and perhaps of lesser concern, you can only compare groups of the same number of shots to each other. If you shoot a 5-shot 1-MOA group with one gun and a 3-shot 1-MOA group with another, which is more accurate? What would you expect either gun to do if you shot a 10-shot group?
Finally, how do you really use the information provided by the group size method for determining practical accuracy in the field? For example, if you have a gun that averages .75-MOA 5-shot groups, what's the statistical probability that a shot taken at 300 yards will strike a target 6 inches in diameter? There's no way of answering that question unless you have more information - and that information is available to you if you want to use it.
Oh - one more. How do you use the information from your group size to adjust your sights so the gun is hitting where you want it to at the distance you're shooting at - not by guess and by gosh, but properly and rationally?
There is a better way, but like most better ways it involves a bit more work. Here's how I evaluate my groups:
Fire a group of any size at an aiming point, then use a ruler (I find digital calipers are actually easier) to measure the distance (i.e., the distance from the aiming point to the center of the shot hole) horizontally (on the x-axis) and vertically (on the y-axis) of every shot. Following the established procedure for cartesian coordinate systems, shots to the left of the aiming point take a negative distance on the x-axis, and shots below the aiming point take a negative distance on the y-axis. You end up with the coordinates of every shot location on a two-dimensional plane.
With that information, you're set up to really evaluate what your gun is doing. The group center is simply the average of the x-axis measurements and the average of the y-axis measurements. So, for example, if you end up with (1.5 inches, -.5 inches) then you know that your gun is shooting, on average and with no guessing, 1.5 inches to the right and a half inch to the left. Using that information you can adjust your sights exactly.
Then, using the Pythagorean theorem, you can calculate the distance of every shot from the group center that you just determined. To do that, you simply subtract the x-axis position of the group center from that of the shot in question, then do the same for the y-axis position, square both quantities and add them together, and then take the square root. All very easy to do with a calculator or, better still, if you set up an Excel spreadsheet.
Once you have the deviation from center for each shot, you can calculate the average deviation, which is a much better evaluation of accuracy than group size, and suffers from none of the problems that I laid out earlier. And, although it's a bit beyond this discussion, using some basic statistics, you can use the standard deviation of the group of deviations from center to determine the probability of striking any size target at any range.
The first is that, no matter how large your group, you're essentially only using the information provided by the two shots that fall farthest apart. There's much more information available if you can somehow factor in what the other shots are telling you.
Second, the group size is unavoidably linked to the number of shots you fire - on average, 3-shot groups from the same gun must be smaller than 5-shot groups, which must be smaller than 10-shot groups, etc. Related to that is the fact that the group can never get smaller as you add shots to it, only larger. There's something inherently unsatisfying about that.
Third, and perhaps of lesser concern, you can only compare groups of the same number of shots to each other. If you shoot a 5-shot 1-MOA group with one gun and a 3-shot 1-MOA group with another, which is more accurate? What would you expect either gun to do if you shot a 10-shot group?
Finally, how do you really use the information provided by the group size method for determining practical accuracy in the field? For example, if you have a gun that averages .75-MOA 5-shot groups, what's the statistical probability that a shot taken at 300 yards will strike a target 6 inches in diameter? There's no way of answering that question unless you have more information - and that information is available to you if you want to use it.
Oh - one more. How do you use the information from your group size to adjust your sights so the gun is hitting where you want it to at the distance you're shooting at - not by guess and by gosh, but properly and rationally?
There is a better way, but like most better ways it involves a bit more work. Here's how I evaluate my groups:
Fire a group of any size at an aiming point, then use a ruler (I find digital calipers are actually easier) to measure the distance (i.e., the distance from the aiming point to the center of the shot hole) horizontally (on the x-axis) and vertically (on the y-axis) of every shot. Following the established procedure for cartesian coordinate systems, shots to the left of the aiming point take a negative distance on the x-axis, and shots below the aiming point take a negative distance on the y-axis. You end up with the coordinates of every shot location on a two-dimensional plane.
With that information, you're set up to really evaluate what your gun is doing. The group center is simply the average of the x-axis measurements and the average of the y-axis measurements. So, for example, if you end up with (1.5 inches, -.5 inches) then you know that your gun is shooting, on average and with no guessing, 1.5 inches to the right and a half inch to the left. Using that information you can adjust your sights exactly.
Then, using the Pythagorean theorem, you can calculate the distance of every shot from the group center that you just determined. To do that, you simply subtract the x-axis position of the group center from that of the shot in question, then do the same for the y-axis position, square both quantities and add them together, and then take the square root. All very easy to do with a calculator or, better still, if you set up an Excel spreadsheet.
Once you have the deviation from center for each shot, you can calculate the average deviation, which is a much better evaluation of accuracy than group size, and suffers from none of the problems that I laid out earlier. And, although it's a bit beyond this discussion, using some basic statistics, you can use the standard deviation of the group of deviations from center to determine the probability of striking any size target at any range.
This is correct.
Traditionally, meaning the custom began many decades back, folks would shoot 5 rounds. The best 3 of the 5 will tell you what the gun and ammo can do. The total of the 5 let you know what the gun, the ammo and the shooter can do. This means that usually 2 of 5 rounds will be tossed a bit by the shooter or the gun and ammo.
tipoc
Gentelmen
This is a great forum ,the debate is healthy and very informational.
So to get my information i will do the 5 shot group. I will use a target that measures 5.5 in (lf to rt & top to bottom) with a center ring measured the same way of 3.0 inches. I will measure the best 3 of 5 shots that land the farthest to the left to the farthest to the right. I want to gauge my ability in the correct way. I am just an average shooter seeking knowledge. My goal is to place as many shots as possible in the 3in ring with slow or rapid fire when I'm shooting.
This is a great forum ,the debate is healthy and very informational.
So to get my information i will do the 5 shot group. I will use a target that measures 5.5 in (lf to rt & top to bottom) with a center ring measured the same way of 3.0 inches. I will measure the best 3 of 5 shots that land the farthest to the left to the farthest to the right. I want to gauge my ability in the correct way. I am just an average shooter seeking knowledge. My goal is to place as many shots as possible in the 3in ring with slow or rapid fire when I'm shooting.
If you want to measure a group correctly, you'll forget about the "Ayoob" method of not counting "flyers". Measure the center-to-center of the two shots farthest from each other in the five-shot group. What the heck's the use of firing five shots for groups, if you're going to "cherry-pick" the best three?? 