Best number of shots per group?

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  • Last Post 13 July 2015
John Alexander posted this 10 July 2015

The Am. Rifleman has set sort of a standard of using the average of five five shot groups  in all their accuracy testing of new guns for the last several decades.  Of course, that often isn't enough groups to find  the difference between the two conditions being tested unless that difference found is fairly large.

There is no law that says you have to use the NRA standard.  Most gunzines don't.  Three shots groups make the product look better and pleases their advertisers. Even better they sometimes quote the best three shot group.  That of course means almost nothing.  Most of us test guns and loads to find answers not to make our guns or ourselves look better

Since only the two widest shots determine group size. The other shots are sort of wasted. (33% in a three shot group up to 92% in a 25 shot group) It seems to me  the most efficient number of shots per group to get the most information out of our shots is clearly a series of two shot groups fired at multiple aiming points. Every shot counts.

The average of the two shot groups could then be converted to the equivalent size for 3, 5, 10, or 20 shot groups by known factors.  Or as RicinYakima has suggested, finding actual composite groups by leaving up a backer target for the number of shots to find a ten or twenty shot group.  

What do you think?  For those folks that seem to shoot only a few  shots in their testing the efficient two shot group would get them the most information for their money.

John

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TRKakaCatWhisperer posted this 10 July 2015

I know one fellow that shoots ONE round from a cold barrel.

One shot and 10-15 minutes cooling time.

His 10 shot groups are GOOD!

Gives him first-shot confidence.

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RicinYakima posted this 10 July 2015

TRK, If I were a hunter, one one-shot group is enough. But worthless for a match shooter who has to shot 2 ten-shot groups in 30 minutes.

John, I know I am not going to change the world, but the old “String” measure is my favorite. The total distance from the center to the edge of each bullet hole. Every shot counts.

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LWesthoff posted this 10 July 2015

Long time ago, I remember reading that some mathematition/manufacturers of ammunition and/or firearms had determined that it required a 7 shot group to determine accuracy.
I still stick with a string of 5 shot groups. Maybe my wife is right when she says I'm kind of stubborn.

Wes

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TRKakaCatWhisperer posted this 10 July 2015

RicinYakima wrote: TRK, If I were a hunter, one one-shot group is enough. But worthless for a match shooter who has to shot 2 ten-shot groups in 30 minutes.

...

I agree.

I do 10 shot groups - as fast as I can fire - for 'prairie dog accuracy' - because you are presented with so many targets all at once.

 

 

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John Alexander posted this 10 July 2015

I agree with Ric that String measurement is a way for every shot to count in the assessment IF what you want to measure is how well you are hitting to the center of the target. 

 If I understand it correctly it gives a value for both accuracy and how well the rifle is zeroed. The mean radius method is similar only it gives a measure of the accuracy whether the zero is perfect or not.

I think the main reason that group size is the dominate method used is because it is easy to do and easy to understand.  That probably is changed some now if you have the equipment and computer software.

John

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nimrod posted this 10 July 2015

I like the string measurement it is starting to come back in some muzzle loading events it does tell all. For some time I have played around with a X,Y system multiply the vertical measurement times the horizontal I think that it gives a more meaningful measure of the group size than just the widest measurement.

RB

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norm posted this 11 July 2015

One winter when I was real bored I took my fired production class targets from the past year and measured from the x dot to the bullet hole on each record bull then added the measurements together. Surprise! sometimes a 46 or 47 would have a shorter total than a 49!

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JeffinNZ posted this 11 July 2015

It depends on the application.

For a large game hunter a 3 shot group is more than enough as that would likely be the most they would fire at one time.

For a varmint shooter 5-10 rounds. Same for target.

Horses for courses.

Cheers from New Zealand

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John Alexander posted this 11 July 2015

Nimrod, Your thoughts were shared by the founders of the CBA.  In he earliest CBA postal matches X and Y were reported instead of distance between widest shots.  It wasn't clear how they decided a winner, but I assume it was by minimum area as you suggest. I also sometimes measure both X and Y to get a sense if vertical stringing is a problem.

Norm, The results you observed could happen even if all groups were perfectly centered.  A lot of solid shots well within the scoring ring on one target and a a lot of “just made it” shots on the other.  However, one group being centered and the other with the group's center a distance from the X dot may be the more likely culprit. String measurement  using the center of the target obviously depends on both dispersion and how well centered the group is.

John

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Tom Acheson posted this 11 July 2015

Is the “string thing” for match shooting only? We usuually shoot our group targets before the score targets so shooters can have an opportunity to adjust their scopes to be “centered” in preparation for the score event.

And....how about range testing various new loads where you know the scope is not adjusted for the “perfectly centered” situation and you want to compare groups to make decisions about the next loads to try?

Are there two different “worlds” being discussed here?

Tom

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John Alexander posted this 11 July 2015

Using the string approach by measuring from the center of the target obviously is meaningless unless that groups are pretty well centered around the ten ring.

This has been an interesting discussion but not a peep out of any of you about my contention that shooting a series of two shot groups could be the most efficient way (all shots contributing to results) to assess accuracy (OK precision) and still be easy to do and understand. Just too crazy to to comment on politely?

John

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frnkeore posted this 12 July 2015

John Alexander wrote: Using the string approach by measuring from the center of the target obviously is meaningless unless that groups are pretty well centered around the ten ring.

This has been an interesting discussion but not a peep out of any of you about my contention that shooting a series of two shot groups could be the most efficient way (all shots contributing to results) to assess accuracy (OK precision) and still be easy to do and understand. Just too crazy to to comment on politely?

John I'll take a stab at it. If that was the match format, you would still have a winner, that winner would, most likely still be the most accurate and as many places as there are shooters behind the winner. It wouldn't show bedding and barrel heating issues, near as well as five shots.  When testing, I don't like two shots, they can't tell you very much, random luck will enter the equation. A one shot ladder test would probably tell you more and would make a interesting match, too :). When testing, if I don't get a flier, in three shots, I go on to at least five but, I've gotten many good two shot groups, close to each other and by the third shot, abandoned the group. Just some random thoughts. Frank

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RicinYakima posted this 12 July 2015

John, From my point of view, if you shot two shots, they show their relationship. If you shot three shots, each one is related to the other two (six relationships). If you shoot 100 it is 100 to the 99th power relationships. One 25 shot group is worth 25 to the 24th power, much more than 10 two-shot groups (10 relationships). FWIW, Ric

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joeb33050 posted this 12 July 2015

2 shot groups Brent Danielson has championed 2 shot groups for accuracy testing for years. He is a professor at U Iowa?, knows much about paper patching, swaging bullets, LRML, etc; and almost as much about statistics as he thinks he does.I do NOT disagree with his 2 shot group method for statistical reasons, but because: A. 5 shot groups are common, and comparison is easy. We DON'T have ready comparisons of 4 or 6 or 2 or 8 shot groups. B. Shooting from the bench and moving the rifle from bullseye to bullseye on a target very often makes the zero change. A group low/left--move rifle to new bullseye, a group low/center, for example. This happens because of the bench rest/bag/rifle setup, changing the aim point changes pressures on the gun by br and bag. Maybe very experienced br shooters can avoid this, but I see it in my shooting on occasion. Thus, changing aiming point often, for 2 shot groups, may introduce zero shifts; and we don't know if we're measuring group size or zero shifts. Each bullet hole contains information about accuracy, whether in 2 or 3 or 5 or 10 shot groups.  It is incorrect to contend that only 2 holes in a 5 shot group provide information about accuracy, each of the five holes provides the same amount of information.

There is no “right” number of shots per group, a set of “n” shots contains information no matter how they're divided.  

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joeb33050 posted this 12 July 2015

String measure Other shooters look at my targets and offer suggestions, sometimes correct, about changing sight settings to get the gun shooting center.  I've explained many times that when shooting groups I set the sights to shoot away from the center; else I'd shoot the center and have nothing left to aim at.  I've also explained that many shooters, shooting for score, aim at some point other than center and adjust the sights to hit center.  But we all know that. String measure works fine for guns shooting 3” 200 yard groups, aiming at center. For our guns, shooting teeny groups, we'd have to have aim point different from impact point.  I don't anticipate a CBA shift to string measure any time soon.

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Tom Acheson posted this 12 July 2015

Sometimes I don't “log out” and it looks like on the forum for hours at a time .......but not so!

Maybe unrelated here in this exchange but at a match 10-years ago someone said...."anybody can get lucky and shoot a small 5-round group but the real test is a 10-round group"

Tom

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John Alexander posted this 12 July 2015 

      Lots of good comments and the kind that encourages one to “think about it.”

   As usual, I never write things as clearly as I intend to.  I had no intention of proposing two shots at several aiming points as a match format just as an efficient and easy way to assess the accuracy of a rifle/load.  However, Frank's comments got me thinking about the match possibilities.  Not all shooters would think that a crazy idea.  If I'm not mistaken at least one of the rimfire benchrest games shoots each shot at a different aiming point.    Frank notes correctly that a two shot group (singular) doesn't tell you much.  A 3 shot group is better and a 5 shot group is better yet etc. etc. right to at least a 100 shot group which has more information in it than any ONE of the lesser single groups   To me the important question isn't which size individual group is better if you are only going to shoot one group. The answer obviously is the single group with more shots in it is going to tell you more than the single group with fewer shots.  I assume we can all agree on that.  The question I was thinking about is what is the most efficient way to get the most information out of say 20 shots.  After all we all have our spending limit in time, patience, or money when we go out to try to assess whether 20 gr. of Smokum powder is better than 22 grains.    Joe is right changing from one bull to the next can change your zero which wouldn't matter since you are only measuring the distance the two shots.  It is not so clear that it changes your accuracy level, which would indeed matter, unless you have really bad setup. Apparently those rimfire shooters cope with it well so maybe the difficulties are not so great.    Your comments stirred up the remaining neurons in my brain and I am still thinking but I want to get to some outside work before it gets too hot.  More crazy thoughts later.    John

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PETE posted this 12 July 2015

John,

Your right. POA or sight changes are not really that bad when moving from one bull to the other.

In ASSRA .22 RF competition we shoot at a 6 bull target at 100 yds. One bull is the sighter the other five are for record and you shoot two shots on each record bull for a total possible score of 250-10c.

What I've found is that if your centered up well on the sighter and everything's going your way the shots will just wander around the 3/4” 25 ring. As in any other score target wind and mirage will get you before you a needed change in sights are needed. Happened to me yesterday. Shot a 247-7c. The three 24's were a condition I didn't catch. There have been several 250's shot over the years.... none by me tho. :)

It's a lot easier shooting 250's at 200 yds. as you just have to put the 10 shots into a 1 1/2' 25 ring. In the last two years another guy and I are tied at two 250's apiece. But I consider the other guy the better shot. He shot his with a .25/20SS and I shot mine with a .32/40.

As for the number of shots that are best to determine a good load or not... When testing I shoot 5 shot groups. Whn I have a coupla good looking loads I shoot a coupla 10 shot groups and whichever shows the best that'll be my “best” load for that gun. I do this for both rifle and handguns.

Pete

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joeb33050 posted this 13 July 2015

Tom Acheson wrote: Sometimes I don't “log out” and it looks like on the forum for hours at a time .......but not so!

Maybe unrelated here in this exchange but at a match 10-years ago someone said...."anybody can get lucky and shoot a small 5-round group but the real test is a 10-round group"

Tom"A” five or ten shot group tells us somewhere between little and nothing. A set of 5 five-shot groups tells us a zillion times more, and few shooters get lucky for 5 groups in a row.

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TRKakaCatWhisperer posted this 13 July 2015

joeb33050 wrote: 2 shot groups Brent Danielson has championed 2 shot groups for accuracy testing for years. He is a professor at U Iowa?, knows much about paper patching, swaging bullets, LRML, etc; and almost as much about statistics as he thinks he does. ....  

Iowa State University

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