I tested some more 52 grain Barnes Match Burner loads today, but from a different rifle. The results were basically the same as last time. The difference between groups was less than 0.1". These were not cold bore shots, but I'd only shot 5 shots of a different load through the barrel before shooting the BMB group. With very similar results using the same load from two different rifles, how confident can I be that this load is a good one? By good, I mean one that will generally shoot under 1.5" from 100 yards? Not always, but most of the time.
5 shot groups "kinda worthless"?
- Thread starter Cityevader
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denton
Member
Well, OK then. We'll have to go back and edit all the stats books that explain the d2 constant, which is the conversion factor between SD and range, which is what many shooters call ES.
these are two targets, shot on the same relay, by two Smallbore Prone National Champions. The distance is 50 yards.
There are very good reasons to have five shot targets in competition, and it has to do with scoring. With shooters of this skill level, it can be virtually impossible to tell if there are five rounds in that hole, never mind ten.
the meter target is a particular pain to score. Try fairly determining a ten shot shot that blows out the center.
I have these F Class buds who blow chunks out of the center of the 100 yard bull. So how do you score a target when you cannot verify there are ten shots on the target?
these are targets shot prone with a sling, at a 100 yard reduced Highpower match. These targets were fired by a former 1000 yard Wimbleon Cup winner.
How do you score a target like this?. How many X's would you assign to the score? How do you verify there are 20 rounds on target?
I scored a two time 2700 Bullseye National Champion. He shot clusters. I aggravated him by telling him that he needed to spread the shots out as I was having problems finding all ten on the target. Luckily, I lived to the end of the day.
this is his 22lr composite group, on the bottom target. Just imagine that it gets hard to tell if there are 8, 9, or ten shots in a group.
That's why they have five shot targets in some shooting sports, not that five shots is a measure of accuracy and consistency. Nope, it all has to do with finding the holes.
JerkyFreak
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Why not just explain what the "d2 constant" is and how it is used here then we can all learn.
denton
Member
Sure. No problem.
A couple of caveats first: 1. When we shoot a few shots and figure out the mean or standard deviation, we're using a sample to estimate what the long term, whole process looks like. Because there is uncertainty in those estimates, different ways of making the estimate will come up with different estimates. Only The Almighty gets perfect information. 2. All of this assumes that "assignable cause" or "special cause" has been eliminated. If you're target shooting, those would be things like shooter flinch, barrel rubs, loose hardware, etc.
Range (ES), variance, standard deviation (SD), semi-interquartile range, RMS deviation, and a few others are all estimates of how spread out the data are.
Standard deviation will typically underestimate variation if the sample is small. Range doesn't have that problem. So for small groups of data, range is usually better than SD. If there are 10 or more data in the group, then SD is better.
If you want to convert from range to SD, you divide by the d2 constant, which depends on the number of data in the group, N.
N.....d2
2.....1.128
3.....1.693
4.....2.095
5.....2.326
6.....2.534
7.....2.704
8.....2.847
9.....2.970
10...3.078
Example, 5 muzzle velocities (keeps the math simple):
2950
2938
2972
2948
2960
The standard deviation is 12.92, but since the sample is so small, the truth could easily be anywhere between 7.74 and 37.11.
The range is 34. Dividing by 2.326, we get another estimate of SD, 14.6.
Good info.
The difference between the two methods is 1.68fps! We are deep in the weeds my friends. Great fun intellectually but, hardly practical.
JFrank
Member
Slam fire asked- How do you score a target like this?. How many X's would you assign to the score? How do you verify there are 20 rounds on target?
I wouldn’t know how the rim fire crowd scores their targets or why they decided on the course of fire. I only feel clear on what we are doing in long range Benchrest by shooting 5 shots for 17 lb class and 10 shots at heavy gun. In short range I’ve over heard talk of moving backers but no personal experience, perhaps a case for shot marker program and E targets that the F class guys are adapting.
I wouldn’t know how the rim fire crowd scores their targets or why they decided on the course of fire. I only feel clear on what we are doing in long range Benchrest by shooting 5 shots for 17 lb class and 10 shots at heavy gun. In short range I’ve over heard talk of moving backers but no personal experience, perhaps a case for shot marker program and E targets that the F class guys are adapting.
JerkyFreak
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If I understand correctly it is a method to estimate what the SD would be if faced with an ideal set of data. Like a shortcut to a close enough answer.
Not a conversion factor though.
It's not a conversion factor, it's another method to estimate SD that will work if the stated assumptions apply.
The typical calculation for SD is also an estimate of SD unless you are calculating the SD of the entire data set. We aren't using the entire data set in this case because we are choosing a sample (a certain number of shots) to represent the actual underlying distribution that governs all the possible shots that could result from that loading and firearm, not just the ones (3 or 5 or 25 shots) that were actually fired in testing.
For example, if you want to know the SD of the age of the next 100 people you meet, you can collect the age data for the next 100 people you meet and use the SD calculation and that is the actual SD for those specific 100 people. On the other hand, if you want to know the SD of the age of EVERYONE in a town of 10,000 people and you get the age from a random 100 people in the town and use the SD calculation on that set of 100 people, you're estimating the SD of the age the town. You could calculate the SD of the town instead of estimating it if you had the age of every single person in the town but that would be 100 times more work.
The point of shooting groups is to generate a sample that will provide insight into the actual accuracy of an ammunition gun combination. It's not really that important what the SD of 3 shots is, what you really want to know is what the overall SD of that loading will be so you can see if it's performing to your expectation--so that if you use the ammunition in a match where you need to shoot 50 rounds, you have an accurate picture of what the result will be. You can ESTIMATE the SD of the ammo by shooting a SAMPLE of it (5 or 25 shots, or 5 groups of 5 shots, or whatever) and then doing the typical SD calculation to get the estimate of the SD for the entire batch. Or you can ESTIMATE the SD of the ammo by shooting a sample of it and using the Range estimate method provided.
The question is: However you do the estimate, how many shots do you need to shoot to get a good characterization of how the ammunition performs?
If you take too few shots, you may believe you know how the ammunition is performing when actually you don't. If you shoot too much, you've wasted time/effort and money/ammo when you could have gotten an adequate answer with less expenditure of time/effort/money/ammo.
The typical calculation for SD is also an estimate of SD unless you are calculating the SD of the entire data set. We aren't using the entire data set in this case because we are choosing a sample (a certain number of shots) to represent the actual underlying distribution that governs all the possible shots that could result from that loading and firearm, not just the ones (3 or 5 or 25 shots) that were actually fired in testing.
For example, if you want to know the SD of the age of the next 100 people you meet, you can collect the age data for the next 100 people you meet and use the SD calculation and that is the actual SD for those specific 100 people. On the other hand, if you want to know the SD of the age of EVERYONE in a town of 10,000 people and you get the age from a random 100 people in the town and use the SD calculation on that set of 100 people, you're estimating the SD of the age the town. You could calculate the SD of the town instead of estimating it if you had the age of every single person in the town but that would be 100 times more work.
The point of shooting groups is to generate a sample that will provide insight into the actual accuracy of an ammunition gun combination. It's not really that important what the SD of 3 shots is, what you really want to know is what the overall SD of that loading will be so you can see if it's performing to your expectation--so that if you use the ammunition in a match where you need to shoot 50 rounds, you have an accurate picture of what the result will be. You can ESTIMATE the SD of the ammo by shooting a SAMPLE of it (5 or 25 shots, or 5 groups of 5 shots, or whatever) and then doing the typical SD calculation to get the estimate of the SD for the entire batch. Or you can ESTIMATE the SD of the ammo by shooting a sample of it and using the Range estimate method provided.
The question is: However you do the estimate, how many shots do you need to shoot to get a good characterization of how the ammunition performs?
If you take too few shots, you may believe you know how the ammunition is performing when actually you don't. If you shoot too much, you've wasted time/effort and money/ammo when you could have gotten an adequate answer with less expenditure of time/effort/money/ammo.
JFrank
Member
Don’t forget to calculate the AM SD separate from the PM SD as the weather warms up the load changes.
You're finding that temperature change results in significant changes to the accuracy (group size) of a given load, beyond just changing the POI? If so, I would think you'd want to try a different loading if extreme accuracy is a concern given the general inability of most humans to control the weather.
JFrank
Member
Nope ya can’t control the weather but you can anticipate and tune accordingly
, I’ll add that in long range BR, a peak tune for five shots in the morning is different from a peak tune for a ten shot string shot in the heat of PM.
JFrank
Member
It can get ugly…
however If a guy tunes a low node/ conservative tune it will normally travel well and not change as much while shooting decent aggs and even score well, but we are there to shoot small groups when conditions allow and peak tunes set records or blow up.
What about shooter error. That’s the big variable. In this discussion that no one talks about. If you are a good consistent shot, 3 to 5 shot groups. tell you all you need to know. If you are a good shot, you know each time you pull the trigger whether it was a good shot or you were not consistent in what you did.
What you all are talking about is only applicable if a machine is firing the rifle.
What you all are talking about is only applicable if a machine is firing the rifle.
Pudge
Member
I think this is an interesting question. If one were to load up, say 30 of the tightest group's load and 30 of the largest group's load and place them in containers such that the shooter didn't know which group of 30 they were shooting, then shoot them consecutively in 6, 5-shot groups like you originally posted, it would be safe to assume that we would have two targets that would average out like the original 6 groups you posted. But if the tight load produced consistently better groups than the wide load, I might be inclined to give more credence to ladder groups than statistical analysis.
denton
Member
Thought about your comment for a bit.... Here are some practical ways to use the d2 constant:
1. Ever wonder how repeatable your chronograph is? Set up two identical chronographs in series, and fire several cartridges across both of them, in random order. Adjust the second one's readings for the expected velocity drop. Now you have matched pairs of data. Take the positive difference in each pair. Average the differences. Divide the answer by the d2 constant for 2 data, and that gives you the standard deviation of the random error in the chronograph. That's your repeatability. I did that with a pair of Shooting Chronys, and they performed well.
2. Working up a load? Make matched pairs of cartridges at 1/4 or 1/2 grain increments. Chronograph them in random order. Again, you have matched pairs of data. Do a scatterplot of MV as a function of charge to see the result. Then take the positive difference in each data pair, average them, and divide by the d2 constant. Now you have the variation of your MV and a nice picture of how much MV the loads produce.
3. If you're shooting 5 shots to get the mean and SD of MV, just skip the calculation of SD. It's not very intuitive for most folks, and the highest speed minus the lowest speed (range) has all the information you're likely to get about variation, and with 5 shots it's a better estimate than SD.
4. If you really want to analyze a target, shoot 5 shots at each of a few targets. For each target, find the center of the group and measure the distance of each shot to it. Subtract the farthest distance from group center from the nearest distance to group center. That gives you a range. Average the ranges of the targets. Divide the average by the d2 constant for 5 data. This gives you a standard deviation for your shot placement. 68% of your shots will fall within plus or minus that number. 95% will fall within twice that number, and 99.7% will fall within three times that number. Those numbers will apply pretty well whether the POIs are normally distributed or not.
All of the above assume that "special cause" has been removed.
So it does lead to some results that would be difficult to obtain otherwise.
.45Coltguy
Member
Not arguing with posters here on how to achieve top accuracy, but, it seems there is some information overload for the average shooter. So, I tend to agree with Casefull on this.
As I no longer hunt and was never really in the bench-rest deal, I just shoot my lever rifles in the desert, so, accuracy is what I make it. Just the way I look at it, but I understand the detailed data for some.
As I no longer hunt and was never really in the bench-rest deal, I just shoot my lever rifles in the desert, so, accuracy is what I make it. Just the way I look at it, but I understand the detailed data for some.
Now there is something I might try. Not the double blind that is the highest standard, but a single blind at least.
Also, for what it's worth now, the test loads are only the ones next to the circles with charge weights next to them. The groups in the center are other loads I've used for a while and wanted to see how they did from a scoped rifle. They'd always been shot from a rifle using aperture sights. The test loads ranged from 22.6 grains down to 21 grains of Shooters World Tactical Rifle pushing an RMR 69 grain BTHP. Same bullet, same powder, same primer (CCI #41).
My disinterest in retesting loads that already exceeded my requirements isn't to say the smaller groups won't balloon up later. However, I already know the larger ones are above what I'm after. If @denton 's assertion is correct from the first page of this thread, and one can expect a five shot group to reflect an actual group maximum of around 50% more than the shot test group size, that's within the goal of the load. Since these are only 4 shot groups, maybe that goes up to 1.6x, and I'm still fine with that. However, if I apply that same spread to the largest group there, about 2.3", then the reduction of 50% means they're still bigger than the others.
LiveLife
Member
Disclaimer: Following post assumes other shooting variables such as scope/mount loosening, receiver movement in stock, shooter input on trigger/stock, wind, etc. are non-issue and only variable is the ammunition.
I think we scared the OP away ... post #3 is the last post from OP and it is specific to 22LR tested at 75 yards.
And at 75 yards of 22LR velocities, bullet drop will start to factor in as vertical stringing/dispersion could be perceived as "flyers" (And why many people prefer 50 yard testing for 22LR).
But if these "flyers" are not shooter induced (Reason why we use lighter match trigger job/kits) or rifle induced (Square bolt face work by CPC for 10/22 or CNC machined Power Custom bolt with captured firing pin to reduce flyers), then the "flyers" are range of muzzle swing and must be factored into overall group size.
During the 10,000+ round test, I was perplexed by repeated small groups produced then larger groups with flyers. I thought it was effect of barrel heating up but when I shot my reference Aguila 40 gr CPRN that produced average 3/4"-1" groups with cold/hot barrel, I realized it was the ammunition, not the barrel heating up.
So how many 5 shot groups need to be shot to capture the full swing of barrel harmonics? Depends on the 5 round random sample you choose from the box. For me, I would like to see group size swing from cold to hot barrel on multiple range trips before I deem capturing full swing of barrel harmonics for a particular ammunition.
Another factor I didn't realize that contributed to group size was shooter fatigue.
I usually shoot 300-600 rounds over couple hours for each range trip and found shooter fatigue definitely affected group size. If I have any doubt, I will shoot a confirming reference Aguila 40 gr CPRN group and if reference group is larger than 1", I take a break before resuming shooting with another confirming reference group (If group size is 3/4"-1", then I continue with range test but if it's larger than 1", I consider calling it a day).
Here's a sample 10/22 50 yard target showing different ammunition groups starting with reference Aguila 40 gr CPRN 10 shot group. As different ammunition produced significantly larger groups, I shot four confirming reference groups to verify it was ammunition for sure and not shooter/rifle - https://www.thehighroad.org/index.p...izing-22lr-on-the-cheap.898035/#post-12145890
Here's a sample T/CR22 50 yard target showing significantly larger Federal 525 round Blue Box compared to 550 round Red Box exclusive to Walmart. To verify group size, a second 525 Blue Box group was shot followed by confirming reference Aguila 40 gr CPRN group and 1" group indicated to me significant jump in group size was due to ammunition - https://www.thehighroad.org/index.p...izing-22lr-on-the-cheap.898035/#post-12146603
This T/CR22 50 yard group got wild and I went "What the heck?". After reference Aguila group, I thought I captured swing range of Thunderbolt and Armscor but subsequent #2 and #3 groups produced different group size. But if the flyers were extreme swing range of muzzle from barrel harmonics, they must be factored in for composite group size in total. I finished the target with confirming Aguila group and except for two flyers at 6/8 o'clock, 8 rounds went into 3/4" size group. (FYI, after CPC bolt work/Power Custom match bolt with captured firing pin, these Aguila "flyers" lessened)
The listing of smallest to larger group size ammunition comparison mentioned on post #8 is from composite of all these documented 5/10 shot groups factored together - https://www.thehighroad.org/index.php?threads/5-shot-groups-kinda-worthless.920275/#post-12654191
And keep in mind that the listing is mostly specific to 10/22 which has shown to be very ammunition selective and I plan on continuing the comparison testing with newer lots of ammunition focused more on T/CR22 and KSA bull barrel.
So for me, 5 shot groups in limited numbers don't provide the whole picture and sufficient rounds must be shot to capture full swing of barrel harmonics for each ammunition tested. (Yes, I considered testing different barrel tuners but that's for another thread discussion)
I think we scared the OP away ... post #3 is the last post from OP and it is specific to 22LR tested at 75 yards.
If you are comparing different brands of 22LR to determine which shoots smaller groups at 75 yards, as I mentioned in post #8 from 10,000+ round test, sufficient groups need to be shot to establish an "average pattern" to determine which ammunition is more accurate - https://www.thehighroad.org/index.php?threads/5-shot-groups-kinda-worthless.920275/#post-12654191
And at 75 yards of 22LR velocities, bullet drop will start to factor in as vertical stringing/dispersion could be perceived as "flyers" (And why many people prefer 50 yard testing for 22LR).
What I learned from shooting 40,000+ rounds while capturing 5/10 shot groups during last 10,000+ rounds from 10/22 and T/CR22 is different ammunition produces varying amount of barrel harmonics/vibration and which 5 rounds you select could exit the muzzle closer to the center axis of barrel swing or outer extremes we call "flyers".
But if these "flyers" are not shooter induced (Reason why we use lighter match trigger job/kits) or rifle induced (Square bolt face work by CPC for 10/22 or CNC machined Power Custom bolt with captured firing pin to reduce flyers), then the "flyers" are range of muzzle swing and must be factored into overall group size.
During the 10,000+ round test, I was perplexed by repeated small groups produced then larger groups with flyers. I thought it was effect of barrel heating up but when I shot my reference Aguila 40 gr CPRN that produced average 3/4"-1" groups with cold/hot barrel, I realized it was the ammunition, not the barrel heating up.
So how many 5 shot groups need to be shot to capture the full swing of barrel harmonics? Depends on the 5 round random sample you choose from the box. For me, I would like to see group size swing from cold to hot barrel on multiple range trips before I deem capturing full swing of barrel harmonics for a particular ammunition.
Another factor I didn't realize that contributed to group size was shooter fatigue.
I usually shoot 300-600 rounds over couple hours for each range trip and found shooter fatigue definitely affected group size. If I have any doubt, I will shoot a confirming reference Aguila 40 gr CPRN group and if reference group is larger than 1", I take a break before resuming shooting with another confirming reference group (If group size is 3/4"-1", then I continue with range test but if it's larger than 1", I consider calling it a day).
Here's a sample 10/22 50 yard target showing different ammunition groups starting with reference Aguila 40 gr CPRN 10 shot group. As different ammunition produced significantly larger groups, I shot four confirming reference groups to verify it was ammunition for sure and not shooter/rifle - https://www.thehighroad.org/index.p...izing-22lr-on-the-cheap.898035/#post-12145890
Here's a sample T/CR22 50 yard target showing significantly larger Federal 525 round Blue Box compared to 550 round Red Box exclusive to Walmart. To verify group size, a second 525 Blue Box group was shot followed by confirming reference Aguila 40 gr CPRN group and 1" group indicated to me significant jump in group size was due to ammunition - https://www.thehighroad.org/index.p...izing-22lr-on-the-cheap.898035/#post-12146603
This T/CR22 50 yard group got wild and I went "What the heck?". After reference Aguila group, I thought I captured swing range of Thunderbolt and Armscor but subsequent #2 and #3 groups produced different group size. But if the flyers were extreme swing range of muzzle from barrel harmonics, they must be factored in for composite group size in total. I finished the target with confirming Aguila group and except for two flyers at 6/8 o'clock, 8 rounds went into 3/4" size group. (FYI, after CPC bolt work/Power Custom match bolt with captured firing pin, these Aguila "flyers" lessened)
The listing of smallest to larger group size ammunition comparison mentioned on post #8 is from composite of all these documented 5/10 shot groups factored together - https://www.thehighroad.org/index.php?threads/5-shot-groups-kinda-worthless.920275/#post-12654191
And keep in mind that the listing is mostly specific to 10/22 which has shown to be very ammunition selective and I plan on continuing the comparison testing with newer lots of ammunition focused more on T/CR22 and KSA bull barrel.
So for me, 5 shot groups in limited numbers don't provide the whole picture and sufficient rounds must be shot to capture full swing of barrel harmonics for each ammunition tested. (Yes, I considered testing different barrel tuners but that's for another thread discussion)
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Cityevader
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Nope, I've not been scared away!
I originally posted because 30+ years ago i used to be smart, taking physics, chemistry, alebra 2 as a freshman...math is lovely to me, even if I don't fully understand each individual area of it (such as statistics) it still has an organic, that-makes-sense-vibe that i love.
As for ballistics, i find it amazing that so much is repeatable and predictable while conversely SO MUCH of those equations are wildly variable (unless a machine is in control.)
I am a noobie to guns since only 2020.
I am fascinated by the variability of .22 ammo (5 of my 7 arms are .22.) Hence this topics appeal for me.
I originally posted because 30+ years ago i used to be smart, taking physics, chemistry, alebra 2 as a freshman...math is lovely to me, even if I don't fully understand each individual area of it (such as statistics) it still has an organic, that-makes-sense-vibe that i love.
As for ballistics, i find it amazing that so much is repeatable and predictable while conversely SO MUCH of those equations are wildly variable (unless a machine is in control.)
I am a noobie to guns since only 2020.
I am fascinated by the variability of .22 ammo (5 of my 7 arms are .22.) Hence this topics appeal for me.
Cityevader
Member
- Joined
- Oct 27, 2022
- Messages
- 57
Oh!
Best memory so far... plinking .22 (Savage 64 with 4x Tru-Glo scope) at about 20 yards in the forest when the sun shone through a gap in the trees close to the target.
WHAT AN EYE OPENER!!!!
Within that 5yd sunlit gap, the bullets were obviously visible in flight and holy moly, were they all over the place!
The 5" steel went ping each time but the flight path was left, right, spiralling left, spiralling right, swooping, and arcing, and knuckle-balling. Each path was wildly different but almost every one hit the target.
That was a fun 15 minutes of observation!
Best memory so far... plinking .22 (Savage 64 with 4x Tru-Glo scope) at about 20 yards in the forest when the sun shone through a gap in the trees close to the target.
WHAT AN EYE OPENER!!!!
Within that 5yd sunlit gap, the bullets were obviously visible in flight and holy moly, were they all over the place!
The 5" steel went ping each time but the flight path was left, right, spiralling left, spiralling right, swooping, and arcing, and knuckle-balling. Each path was wildly different but almost every one hit the target.
That was a fun 15 minutes of observation!
Styx
Member
- Joined
- Dec 11, 2014
- Messages
- 3,282
Guess I'm the oddball who doesn't give a darn about being able to get all my rounds through the same hole. If I can get all my rounds on the target within the head and chest area at a self-defense distance, that's all I care about. If I was shooting in a target competition then my goal would change. I don't understand the obsession with groups out of a firearm meant for self-defense. IMHO, it's silly, and sometimes I don't think about or care about unless I'm just trying to impress others at the range.
