VA_XTC_Shooter
Silver $$ Contributor
Yes, it's in Litz's Modern Advancement Book Vol 2. I'll look it up when I get home. He has estimator from 3 to 5 to 10 and maybe 20 shots.
Converting 3-shot group size to 5- and 10-shot group size
- Thread starter South Pender
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VA_XTC_Shooter
Silver $$ Contributor
3 shot scale to 5 shot, multiply by 1.28; to 10 shot multiply by 1.58; to 20 shot multiply by 1.85
5 shot scale to 10 shot, multiply by 1.24; to 20 shot multiply by 1.45
Based on years of experience, I personally would not go into full scale production of reloads based on a single 3 shot group. I like to have confirmed data on the load I select before I start turning out reloads for an upcoming varmint / predator season.
As I stated in a prior post, I have used 3 shot groups to "bracket" a potential load. But I shoot several more groups to confirm the reliability of the results on target. In the past, I have hit a successful load on an initial 3 shot test group (confirmed with several more) and sometimes, although the first group looked good, subsequent testing revealed that it was not as good as first indicated.
Mulligan
Silver $$ Contributor
Triangle Groups
What are your thoughts on triangle groups. I know most look for horizontal groups and some like round. If you found a good rifle load and it prints triangle groups what direction would you approach to take out the vertical. You have a good powder charge with good ES and groups are in the .4 to...
forum.accurateshooter.com
Check out post #9 from the late Donovan Moran
CW
edit
I figured out how to copy this graph from Donovan's post.
I think Moran is talking about something else--relative efficiency (which needs an explanation). This appears to be unrelated (or related in some way that isn't apparent) to the question of converting group sizes.
The figures given by VA XTC Shooter from Bryan Litz's book would seem to answer the question.
divingin
Gold $$ Contributor
Well, IMO, it is a 1MOA rifle for those 3 shots. For the rest, you have to shoot it and see.
To put it another way: the first 3 shots of a 5 or 10 shot group may be at 1.4", or may go into one bullet diameter hole. Since it's the cumulative spread, you have to shoot the rest to see what you end up with. It may well be that the one-hole 3 shot group is followed by a shot well out of that group, or it may go through the same hole.
jackieschmidt
Gold $$ Contributor
My 6PPC Rail Gun is well capable of putting 10 shots in a sub .200 group at 100 yards.
But if I keep putting bullets in that group, it will no doubt in time grow to twice that big.
Keep in mind, reality dictates that once you get passed all of the graphs and theory’s, there are only a few things that will cause a bullet to take the exact same path to the target as the one preceding it, and about a million things that will keep it from doing that.
But if I keep putting bullets in that group, it will no doubt in time grow to twice that big.
Keep in mind, reality dictates that once you get passed all of the graphs and theory’s, there are only a few things that will cause a bullet to take the exact same path to the target as the one preceding it, and about a million things that will keep it from doing that.
In load development we frequently want to know if load A is more accurate than load B. Statistical analysis can help provide an answer to this question. The number of shots required for a meaningful answer depends on the statistical variance between A and B and the statistical confidence level that you choose. The smaller the variance between A and B the more data that is required for a meaningful answer. Also, the higher the statistical confidence level you desire the more data that is required. A statistical confidence level of 95 means that the probability is 95% that A is different than B but that also means that there is a 5% chance of being wrong. While a 98% confidence level has only a 2% chance of being wrong. The principles of statistics will guide you as to how much data you need to achieve your choice in confidence levels.
Although a basic understanding of statistics and statistical analysis is helpful in group analysis, books on the subject are not easy to master. If you have a good high school or college background in math, give the subject a try or better yet find a friend that can teach you.
I have done considerable load development for National Match Course competition (aka XTC). For load development for this application, I shoot 10 shot groups. I see where others doing load development for various applications report mostly using three, five or sometimes seven shot groups but rarely 10 shot groups. Their approach to load development may be appropriate for their application however using insufficient data for analysis for any application can lead to incorrect conclusions.
It has been shown that for long run averages 20 shot groups can be expected to average 1.79 times as large as three shot groups and 1.45 times as large as five shot groups but only 1.17 times as large as 10 shot groups, therefore, I choose 10 shot test groups for XTC load development.
While shooting XTC load development groups, I have observed the hits as the groups develop and sometimes the first three shots are very close together but after all 10 shots are fired the group is usually just another average 10 shot group for that load. Sometimes this is true for the first five shots as well but not as often as for three shots as would be expected. I think this supports my decision to go with the 10 shot test groups rather than three or five shot test groups.
There is also a tendency to throw out “flyers” when firing groups for accuracy testing. Sometimes I see wide shots that at first look like flyers but after the 10 shot group is in place many times the flyer no longer looks as much out of place. So, I do not ever throw out any flyers. Once I think I have a pet load defined, I shoot multiple ten shot groups with that load and average them and then if any wide shots are indeed not representative of the load, they do not play a significant role in analysis and decisions.
I calculate group size using the “extreme spread” method and also the “mean radius” method. The mean radius calculation values all shots in the test group on an equal basis as opposed to extreme spread which only values the two extreme shots. Extreme spread is more widely used for group analysis, but mean radius is a superior measure of merit and has significant advantages such as reducing the significance of a potential flyer.
Although a basic understanding of statistics and statistical analysis is helpful in group analysis, books on the subject are not easy to master. If you have a good high school or college background in math, give the subject a try or better yet find a friend that can teach you.
I have done considerable load development for National Match Course competition (aka XTC). For load development for this application, I shoot 10 shot groups. I see where others doing load development for various applications report mostly using three, five or sometimes seven shot groups but rarely 10 shot groups. Their approach to load development may be appropriate for their application however using insufficient data for analysis for any application can lead to incorrect conclusions.
It has been shown that for long run averages 20 shot groups can be expected to average 1.79 times as large as three shot groups and 1.45 times as large as five shot groups but only 1.17 times as large as 10 shot groups, therefore, I choose 10 shot test groups for XTC load development.
While shooting XTC load development groups, I have observed the hits as the groups develop and sometimes the first three shots are very close together but after all 10 shots are fired the group is usually just another average 10 shot group for that load. Sometimes this is true for the first five shots as well but not as often as for three shots as would be expected. I think this supports my decision to go with the 10 shot test groups rather than three or five shot test groups.
There is also a tendency to throw out “flyers” when firing groups for accuracy testing. Sometimes I see wide shots that at first look like flyers but after the 10 shot group is in place many times the flyer no longer looks as much out of place. So, I do not ever throw out any flyers. Once I think I have a pet load defined, I shoot multiple ten shot groups with that load and average them and then if any wide shots are indeed not representative of the load, they do not play a significant role in analysis and decisions.
I calculate group size using the “extreme spread” method and also the “mean radius” method. The mean radius calculation values all shots in the test group on an equal basis as opposed to extreme spread which only values the two extreme shots. Extreme spread is more widely used for group analysis, but mean radius is a superior measure of merit and has significant advantages such as reducing the significance of a potential flyer.
The problem with statistics for group size is they assume everything is the same for each shot with no account for wind or tune changes. A shot that gets blown out is not a flyer but most certainly changes the group size. I see little value there with any gun that can shoot better than the value of the conditions. Now, that said, if we have a .5 wind value and a 1.5 inch gun, the stat side of things would be of more value but nobody wants to compete with a rifle that can't shoot better than that.
The misuse of a good thing is no argument against it.
Great analysis, chkunz. Those numbers are very close to Bryan Litz's:
20 shot groups 1.85 as large as 3 shot groups; 20-shot groups 1.45 as large as 5 shot groups.
At least!!
Ccrider
Gold $$ Contributor
I don’t care about averages or statistics. I am concerned with what my gun is doing. I expect it to shoot better than averages when tuned.
When tuned, I expect five shot groups to mirror three shot groups at 100 yards. They may not at times, but it will not be because of the gun.
When tuned, I expect five shot groups to mirror three shot groups at 100 yards. They may not at times, but it will not be because of the gun.
Do you expect 10 shot groups to mirror five shot groups?
Ccrider
Gold $$ Contributor
I have not seen a reason to shoot many ten shot groups. But to answer your question, yes, assuming that poi does not change due to barrel heat or fouling. To the extent that they would not, it would be an indictment on the shooter, not the tuned gun’s capability.
When I say shooter, I mean it in the broadest sense, to include failure to execute the shot, read the wind, or make consistent ammo. There is a lots going on shooting a ten shot string as opposed to shooting 5 that has to be accounted for other than the gun’s capability.
Sometime when you have shot your 3 shot group continue shooting more shots into the group and you will find that the group gets larger.
Ccrider
Gold $$ Contributor
I believe that. I regularly shoot 5 shot groups. Why do they get larger is the question.
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