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Old April 16, 2018, 11:40 PM   #76
JohnKSa
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The average of several 5-shot groups only tells you the average of several 5-shot groups, and that's a completely arbitrary statistic.
I suppose that choosing to fire 5 shot groups and average 5 of them is just as arbitrary as choosing to fire 25 shots into a single group. The result of either one is only representative of the results of that particular procedure.

Similarly, someone firing 40 shots in a single group, or choosing to average three 10 shot groups should expect to find that the results of their arbitrary choices will not be representative of firing a 25 shot group or choosing to average five 5 shot groups.

Of course, all of that is really neither here nor there.

The point is that if you shoot a large number of shots into one group and make one mistake, it is the mistake that is going to dominate the results. If you fire more groups and average the results, a single mistake can only affect one group and the effect of averaging will reduce the impact of that mistake in the overall results.
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If the point is to determine how you, your gun or ammo perform, the most important statistic is the largest group, not the average or the smallest.
If the point is to determine how you, your gun or the ammo perform on average, then the important statistic is the average performance.

If the point is to determine how you, your gun or the ammo perform in the worst case, then, of course, the most important statistic is the largest group.
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There is a problem with taking multiple small samples. They can, by chance, not represent the actual performance you're really trying to test.
The nice thing about the averaging process is that if you take enough samples, the odds become good that the average results are representative of the typical performance for that particular course of fire.

On the other hand, if you put all your eggs in one basket and that result turns out to be atypical, you have spent a lot of work on a result that doesn't tell you much.
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Old April 17, 2018, 12:25 AM   #77
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Originally Posted by JohnKSa View Post

The point is that if you shoot a large number of shots into one group and make one mistake, it is the mistake that is going to dominate the results. If you fire more groups and average the results, a single mistake can only affect one group and the effect of averaging will reduce the impact of that mistake in the overall results.If the point is to determine how you, your gun or the ammo perform on average, then the important statistic is the average performance.
If you are aware of a mistake, the 'called flier', you don't include that shot in the group measurement.

If you make a mistake that you aren't aware of, then how do you label a shot a mistake if you are not aware of it being a mistake? Logic says you can't. You have to include it because it might not be a mistake. It might be an accurate reflection of the gun/ammo.

The only 'mistakes' that count are the ones you know are mistakes, and they should be excluded from the measurement.

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The nice thing about the averaging process is that if you take enough samples, the odds become good that the average results are representative of the typical performance for that particular course of fire.
How many samples do you have to take?
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Old April 17, 2018, 01:29 AM   #78
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If you are aware of a mistake, the 'called flier', you don't include that shot in the group measurement.
If you know for sure you made a mistake AND you know for sure which shot on the target was the mistake then I suppose it would make sense to discount that shot and shoot another one to make up for it. Except of course if the goal is to evaluate the worst case performance, in which case the mistake probably shouldn't be eliminated since it certainly contributed to a worst case performance.

I'm not really in favor of trying to pick and choose which shots to keep and which ones to leave out when shooting groups because...
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If you make a mistake that you aren't aware of, then how do you label a shot a mistake if you are not aware of it being a mistake?
Well said.

There's also the situation where you know you made a mistake but you're not sure which shot on target it is. Maybe the "flier" that is high and right is the mistake you know you made, or maybe it's telling you about an ammo problem or a gun problem, and the actual mistake wasn't actually as bad as you thought it was. Once you start trying to pick and choose shots or groups, then you're never really sure if the numbers are telling you about how the shooting is going or if they're telling you how good you are at throwing away shots or groups to make the results come out the way you want them to.
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How many samples do you have to take?
A simple and effective way to know if you have enough is to stop when the average isn't changing significantly any more. If all the groups are fairly consistent then it will stabilize very rapidly.

Or, you could just pick a number of groups you want to shoot and pick the number of shots per group that seems reasonable to you and go for it. Five shot groups are pretty common for handgun accuracy evaluation and averaging a handful of those should provide decent results. You'll see that approach commonly used in published reviews.

I've seen much larger group shot counts used for accuracy evaluation, but only with machine rests, or when some similar technique is used to take the shooter out of the equation as much as possible.
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Old April 17, 2018, 12:18 PM   #79
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I shoot handgun groups to test ammo and the gun and they are always 5-shot. Using a mechanical rest you still have to change magazines and I always check the torque on the rest when I change mags. If you move the gun in the rest changing mags and/or change torque on the screws it will change the impact point from previous groups which has nothing to do with the performance of the ammo-firearm combination. If the gun shoots a 2" group @ 50 yards and then after the magazine change it shoots a 2.25" group but the group center moved an inch left, the inch move had nothing to do the firearm or ammo but moved because of disturbing the rest. In testing you have to do your best to remove all of the outside variables and get to just the gun and ammo. If I shot 50-shot groups you will be wasting ammo more than getting information. Now if you are testing the rest, your procedures will change to reflect that. YMMV
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Old April 17, 2018, 07:22 PM   #80
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I shoot handgun groups to test ammo and the gun and they are always 5-shot. Using a mechanical rest you still have to change magazines and I always check the torque on the rest when I change mags. If you move the gun in the rest changing mags and/or change torque on the screws it will change the impact point from previous groups which has nothing to do with the performance of the ammo-firearm combination. If the gun shoots a 2" group @ 50 yards and then after the magazine change it shoots a 2.25" group but the group center moved an inch left, the inch move had nothing to do the firearm or ammo but moved because of disturbing the rest. In testing you have to do your best to remove all of the outside variables and get to just the gun and ammo. If I shot 50-shot groups you will be wasting ammo more than getting information. Now if you are testing the rest, your procedures will change to reflect that. YMMV
What kind of mechanical rest are you using? And why do you feel compelled to check the torque after changing mags? Is the rest's grip on the gun so poor?
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Old April 17, 2018, 08:37 PM   #81
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If you know for sure you made a mistake AND you know for sure which shot on the target was the mistake then I suppose it would make sense to discount that shot and shoot another one to make up for it. Except of course if the goal is to evaluate the worst case performance, in which case the mistake probably shouldn't be eliminated since it certainly contributed to a worst case performance.
If a shooter includes known fliers in their group measurement, then it's no longer an accuracy test, it's now an IQ test, and the shooter just failed.

If one is trying to evaluate their worst case performance, they should shoot blindfolded. That would fit the description.

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Originally Posted by JohnKSa View Post

I'm not really in favor of trying to pick and choose which shots to keep and which ones to leave out when shooting groups because....

There's also the situation where you know you made a mistake but you're not sure which shot on target it is. Maybe the "flier" that is high and right is the mistake you know you made, or maybe it's telling you about an ammo problem or a gun problem, and the actual mistake wasn't actually as bad as you thought it was. Once you start trying to pick and choose shots or groups, then you're never really sure if the numbers are telling you about how the shooting is going or if they're telling you how good you are at throwing away shots or groups to make the results come out the way you want them to.A simple and effective way to know if you have enough is to stop when the average isn't changing significantly any more. If all the groups are fairly consistent then it will stabilize very rapidly.
Only known, called fliers can legitimately be removed from group measurements. Guessing which one(s) might be the flier(s) is called cheating, and also fits the description of failing an IQ test.

There is variability even with multiple groups shot from a Ransom Rest, so stability in group size is a bit of a myth. In this article (https://americanhandgunner.com/exclu...city-accuracy/) the author found up to a nearly three-fold difference in group size when shooting 15-shot groups (many more rounds than mere 5-shot groups) from a Ransom Rest.

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Originally Posted by JohnKSa View Post
Or, you could just pick a number of groups you want to shoot and pick the number of shots per group that seems reasonable to you and go for it. Five shot groups are pretty common for handgun accuracy evaluation and averaging a handful of those should provide decent results. You'll see that approach commonly used in published reviews.
Yes, multiple the 5-shot groups are traditional. But that does not mean there isn't a better way.
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Old April 18, 2018, 12:22 AM   #82
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If a shooter includes known fliers in their group measurement...
If one is absolutely certain that a particular shot on the target is a flier then shooting an additional shot in that group and discounting the flier could make sense under some circumstances.

If there's any doubt at all about which shot is the flier, or whether or not the shot really was a flier, then throwing it out might make the shooter feel better and the group smaller, but now there's something other than the shooter's ability, the gun and the ammo contributing to the results.

Just throwing it out without shooting another shot doesn't sense as now the group being evaluated is a smaller number of shots than originally intended which means it isn't comparable to the other groups shot.

And, of course, if the shooter's ability is a big part of what is being tested, then throwing away "fliers" doesn't ever make sense because fliers are clearly saying something about the shooter's ability.
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If one is trying to evaluate their worst case performance, they should shoot blindfolded.
The comment I made about evaluating worst case performance was specifically in response to the comment that "the most important statistic is the largest group". The "largest group" is clearly the worst case performance for that shooting session. Of course there are really stupid things (like shooting blindfolded) that a shooter could do to make the worst case performance even worse--but I'm not sure what that would prove.
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There is variability even with multiple groups shot from a Ransom Rest, so stability in group size is a bit of a myth.
Yes, of course there is variability even from a machine rest. However stability in group size isn't a myth unless one chooses to unrealistically define it as "absolutely no variability in group size". A gun/ammo/shooter combination that consistently shoots 5 shots into, say, 3" groups, plus or minus a quarter of an inch at 25 yards is shooting pretty stable groups even though they're not all identical.

But a shooter whose groups vary by a factor of 2 or 3 clearly isn't shooting stable groups. Could be an ammo problem, a gun problem, a shooter problem or a combination.

By the way, using a machine rest doesn't guarantee accuracy or consistency--it only eliminates shooter error. If the ammo or gun is the problem then there's nothing a machine rest can do to fix the problem.

The article is interesting--the author's main point is that even with very consistent ammunition velocities (and a machine rest), it is still possible to get inconsistent results.

That doesn't mean he's saying that stable groups are always impossible, he's just showing that one can't assume that consistent velocities = consistent accuracy.
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But that does not mean there isn't a better way.
Correct. But it's certainly a better way for performing a typical handgun accuracy evaluation than shooting 25 shot groups by hand and then picking the largest one as being representative.

I do agree that for some kinds of testing (particularly from a bench or using a machine rest) larger group sizes can make a lot of sense.
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Old April 18, 2018, 12:54 AM   #83
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My goodness, JohnKSa, we might be in near total agreement!
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Old April 18, 2018, 12:56 AM   #84
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Obviously there's something wrong! Let me re-read my post and try again.
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Old April 18, 2018, 11:28 AM   #85
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for my purposes (and to borrow a southern phrase)...

"fellahs, ah think y'all are overthinking this a bit...."

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Old April 18, 2018, 11:52 PM   #86
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Interesting article in the May 2017 issue of SWAT magazine. The author tested a 9mm carbine with various ammo, shooting from the bench.

Average 5 shot group sizes at 50 yards were:

Atlanta Arms 115gr JHP--1.55"
Black Hills 115gr +P JHP--1.25"
Winchester 115gr FMJ--1.88"

These groups, scaled to 25 yards would be 0.78", 0.63", and 0.94".
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Old April 19, 2018, 08:50 AM   #87
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I did this test about 10 years ago, with a P210-6 at a 50ft range. Premium 147gr hollowpoints tended to do the best (speer gold dot and whatever winchester was calling theirs at the time) -- I was able to get some 5-shot groups that could be covered with a quarter. I also recall that the 124gr gold dot load was very close to the same, so I ended up using that as a self-defense load. Bulk WWB 115gr practice ammo tended to do much worse, to the extent that groups looked about the same as those coming out of a Glock 19.
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