When developing a load and testing accuracy, what methods do you use for measuring groups? I am new to this and every time I try and lookup instructions I end up with a totally different method. Is there a standard number of shots and measurment scheme that most people use?
Measuring groups
- Thread starter MattB000
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cdrt
Member
I usually shoot a three shot group with the rifle, measure across the widest part and then subtract the diameter of the bullet. So, if it measured one inch across and I was shooting a .243, you're looking at a 3/4" group.
I think that's pretty standard.
With a handgun, I'll probably shoot a five shot group and measure the same way.
I'm sure you'll get some other ideas and methods on this one.
I think that's pretty standard.
With a handgun, I'll probably shoot a five shot group and measure the same way.
I'm sure you'll get some other ideas and methods on this one.
ajax
Member
I like to use 3 or 5 shot groups and then measure from the center of the furthest hole to the next furthest hole. Good shooting.
jr81452
Member
10 shot groups, measure across the widest part and then subtract the diameter of the bullet. the more shots you fire to test a group the more realistic the group will be. they won't be as small as a 3 or 5 shot group but you will have a better understanding of your firearms POA/POI. there is a good link in the rifle shooting section that has a graphic demonstration of "the benefit of 10 shot groups"
consider this: i used to use 5 shot groups for pistol load testing from my ransom rest. after a certain point all the loads started to be the same. then i switched to ten shot groups and now i can see the difference between 180gr XTP or 180gr GDHP at as little as 7 feet. with a 5 shot group i had to go out to 15 yards to measure the difference.
my .02
consider this: i used to use 5 shot groups for pistol load testing from my ransom rest. after a certain point all the loads started to be the same. then i switched to ten shot groups and now i can see the difference between 180gr XTP or 180gr GDHP at as little as 7 feet. with a 5 shot group i had to go out to 15 yards to measure the difference.
my .02
xring44
Member
If I really want to know what my rifle/pistol is doing, I shoot 5 shot groups, measure the group size carefully, staple a new target EXACTLY over the last one, fire 5 more shots, repeat 4 times. Now measure the bottom target, thats what your rifle/ load combination is doing. 20 shots paints a much clearer story than three or five shot groups.
Grumulkin
Member
That a good technique but I would probably do 3 shot groups rather than 5 shots groups. If you repeat this 4 times you still have a lot of shots for statistical validity.
Also, rather than subtract bullet diameter, just determine which two holes are further apart and measure from the far side of one hole to the near side of the next.
I used to measure out to out and subtract one bullet dia. until it was pointed out to me that the hole in the paper is almost always smaller than the bullet fired. For example, a .308 bullet will punch a hole smaller that .308. Now I measure "center to center" or "outside to inside".
Bad Flynch
Member
Measuring groups is both an art and a science. A well-practiced shooter will usually shoot groups that behave according to the laws of statistics. When that is so, the group sizes can be expressed as probabilities.
For the most part, you can get a really good idea of what your rifle and load are doing by firing three, ten-shot groups. The groups can be measured center-to-center or outside-to-outside, but keep it all the same. You can use three, five-shot groups, but the groups will give an average that is about 70% of the size of the ten-shot groups (95% of the time), and that is why the ten-shot groups are a better measure of long-term performance.
Groups are usually measured by casual shooters as center-to-center, but other methods give a better measurement of long-term performance. Outside measurement and baseline measurement do better, but are tough to correlate with your buddies' measurements for bragging rights.
While this is simplifying it too much, do this: make sure that the average of the three, ten-shot groups falls inside of your desired target area. For example, if you have a 1 minute X-ring, then the average of you groups should fall inside 1 minute of angle. If you deer has a heart that is 4 or 5 inches and you expect to shoot it at 200 yards at the most, then you should have a group that will shoot into 5 inches at 200 yards. That will be for a 95% confidence limit.
For the most part, you can get a really good idea of what your rifle and load are doing by firing three, ten-shot groups. The groups can be measured center-to-center or outside-to-outside, but keep it all the same. You can use three, five-shot groups, but the groups will give an average that is about 70% of the size of the ten-shot groups (95% of the time), and that is why the ten-shot groups are a better measure of long-term performance.
Groups are usually measured by casual shooters as center-to-center, but other methods give a better measurement of long-term performance. Outside measurement and baseline measurement do better, but are tough to correlate with your buddies' measurements for bragging rights.
While this is simplifying it too much, do this: make sure that the average of the three, ten-shot groups falls inside of your desired target area. For example, if you have a 1 minute X-ring, then the average of you groups should fall inside 1 minute of angle. If you deer has a heart that is 4 or 5 inches and you expect to shoot it at 200 yards at the most, then you should have a group that will shoot into 5 inches at 200 yards. That will be for a 95% confidence limit.
dodgestdshift
Member
With a revolver, I shoot the full cylinder. Big game hunting rifle 3 shots. Varment rifle at least 5. I measure the distance between the two farthest apart (at the midpoints of the holes).
Picknlittle
Member
I'm partial to one shot groups. They are always tight though nt necessarily where I was aiming. 
Smokey Joe
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The answer
Matt B--As you can see from the varied responses to yr question,
The more shots you shoot, the clearer will be the real picture of yr accuracy under those conditions. I admire Bad Flynch's statistical approach. And I usually use 10 shot groups myself.
The fewer shots you shoot, the more likely you are to luck into a "bragging rights" target.
It depends on what you really want for results of your shooting.
And, as always, the journey is part of the destination.
Matt B--As you can see from the varied responses to yr question,
the answer is a resounding NO!
The more shots you shoot, the clearer will be the real picture of yr accuracy under those conditions. I admire Bad Flynch's statistical approach. And I usually use 10 shot groups myself.
The fewer shots you shoot, the more likely you are to luck into a "bragging rights" target.
It depends on what you really want for results of your shooting.
And, as always, the journey is part of the destination.
ocabj
Member
Your test groups should reflect the amount of rounds you need to fire with that gun in a particular string of fire.
When I test loads for Service Rifle High Power, I like to run 10-round groups. Since the first 3 stages of fire in HP are 10 shot strings of fire each (multiplied by 2 if an 80 round match instead of 50).
Granted, I think if a 5 round group shoots good and you continue to shoot 5 more rounds into that same group; if those last 5 rounds cause the group to open up, it's an issue with the rifle and not the load (ie: barrel flex due to heat, etc). While it doesn't say the load is bad, it will tell you how your rifle will perform in that kind of stress firing.
When I test loads for Service Rifle High Power, I like to run 10-round groups. Since the first 3 stages of fire in HP are 10 shot strings of fire each (multiplied by 2 if an 80 round match instead of 50).
Granted, I think if a 5 round group shoots good and you continue to shoot 5 more rounds into that same group; if those last 5 rounds cause the group to open up, it's an issue with the rifle and not the load (ie: barrel flex due to heat, etc). While it doesn't say the load is bad, it will tell you how your rifle will perform in that kind of stress firing.
Lupara
Member
Back to measuring groups:
+1 for Bad Flynch's statistics. The more shots the better, but there is a reasonal limit to it. According to Speer's ballisticians, 7 shots would be sufficient. Apart from shooting load ladders, I am shooting 10 shot groups to test a loads's overall accuracy. For me this is rather practice shooting than testing. Thus, the ammo is not wasted.
Traditionally, a group size is defined as the distance of a given number of shots within a circle intersecting the centers of the furthest shots. To construct this circle, you connect the centers of the 3 furthest shots and determine the center of this triangle by constructing the median line of two of its sides. Taking the center of the triangle, you draw its circumcircle with a compass and measure its radius. This will be your group size.
However, if the furthest shots form an obtuse angled triangle, is is sufficient to measure the distance of the two furthest shots as the third one would lie within the circumcircle anyway.
I'm using my son's geometry set square to do this.
http://www.rotring.de/www.rotring.com/index.html
+1 for Bad Flynch's statistics. The more shots the better, but there is a reasonal limit to it. According to Speer's ballisticians, 7 shots would be sufficient. Apart from shooting load ladders, I am shooting 10 shot groups to test a loads's overall accuracy. For me this is rather practice shooting than testing. Thus, the ammo is not wasted.
Traditionally, a group size is defined as the distance of a given number of shots within a circle intersecting the centers of the furthest shots. To construct this circle, you connect the centers of the 3 furthest shots and determine the center of this triangle by constructing the median line of two of its sides. Taking the center of the triangle, you draw its circumcircle with a compass and measure its radius. This will be your group size.
However, if the furthest shots form an obtuse angled triangle, is is sufficient to measure the distance of the two furthest shots as the third one would lie within the circumcircle anyway.
I'm using my son's geometry set square to do this.
http://www.rotring.de/www.rotring.com/index.html
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