Accuracy, ES, and SD: why 3 and 5 shots are just not enough, what the data shows...

Accuracy, ES, and SD: why 3 and 5 shots are just not enough, what the data shows...

This is a discussion on Accuracy, ES, and SD: why 3 and 5 shots are just not enough, what the data shows... within the General Firearm Discussion forums, part of the Related Topics category; I was at the range yesterday when another one of my buddies showed up. He shoots a $4300 Desert Tech with a Kahles scope that ...

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Thread: Accuracy, ES, and SD: why 3 and 5 shots are just not enough, what the data shows...

  1. #1
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    Accuracy, ES, and SD: why 3 and 5 shots are just not enough, what the data shows...

    I was at the range yesterday when another one of my buddies showed up. He shoots a $4300 Desert Tech with a Kahles scope that adds probably another $2500 to the rig. This one is chambered in 223/556 - not sure which. So after shooting some, we were talking and I asked what kind of velocity spreads he was getting with his Lapua cases, CCI 450 primers, 24.4 gr of Varget and 77 gr Berger OTM bullets.

    He started going through his DOPE book and the first one we came to was 70 fps, then another at 49 fps, and some lower and we stopped. As we talked he made the comment that the ES doesn't matter if you're getting the accuracy you want/need. And, I agree completely. So why worry with ES and SD at all? Well, the key here is, if you're getting the accuracy you want/need. My friend never shoots longer than 300 yards. So for his shooting requirements an ES of 70 fps is essentially irrelevant - not quite insignificant but not major. I on the other hand, shoot at 500 yards and a velocity spread of 70 fps is much more significant and detrimental to my accuracy and precision wants/needs.

    For example, at 300 yards a 70 fps variation is only going to produce a vertical dispersion of 0.4 MOA. But at 500 yards that same 70 fps would cause a 0.8 MOA vertical dispersion and at 600 yards a 1.07 MOA vertical dispersion. In essence the vertical spread (600 yards) will vary by almost 1.1 MOA due to a 70 fps velocity variation. Three hundred yards to 600 yards is double, i.e. 2x, but the effect on vertical POI shift due to velocity spread is 2.65x.

    So for longer shots, velocity variation does matter, which brings us to the topic at hand, why is 3, 5, even 10 shots not enough to give us an accurate representation of our gun and ammo? Let's put some perspective in here.

    Let's say we watch a guy shoot 3 free throws and he makes two of them, Is that enough to accurately represent his skill? If we accept 3 shots as enough, then he's a 67% free throw shooter. But what if he makes all of the next 7 tries? Now he's a 90% free throw shooter. Which is more likely to be right, 67% based on 3 shots or 90% based on 10 shots? But what if he shoots 5 more and makes 4 of them? Now he's shot a total of 15 shots and made 13 of them. That would make him an 87%.

    The point is, 3 shots aren't enough, nor is 5 shots.

    Over the past few days, I've been doing some primer tests by shooting 20 shots with each primer. I won't make you sift throw the raw data, but what I have done is construct some charts from the raw data that show how ES and SD develop as more shots are fired.

    I started with the ES and SD for just 3 shots, then for 4 shots, then 5, etc. all the way up to 20 shots. I'll start with the CCI 450 primer group. Let's say I shot 3 shots and stopped, i.e. no more shots, and I base my rifle/load on those 3 shots. For my first 3 shots, in the exact order they were shot would show an ES of 11 fps and a SD of 5.6 fps. WOW! Clearly I have achieved my velocity goal! But, I've got two more rounds, I'll shoot them and quit then...............

    The next two rounds drive the ES up a point to 12 fps to and the SD down to 5.2 fps! YeeeHaaa - finally Heck, this is great! I'll shoot 5 more just to celebrate...........Wait a minute now, at the end of 10 rounds the SD has risen to 34 fps and the SD to 10.5 fps, ummm, well, that's still good , certainly not fantastic as the first 5 shots indicated, but still better than good! Since I'm doing so well, I'll shoot 5 more...............OUCH! There goes my great numbers ; ES = 58 fps; SD = 16.1 fps - How does one go from 12 fps and 5.2 fps to 58 fps and 16.1 fps - the ES went up by almost a factor of 5 and the SD by factor of 3.

    What happened? Well, 3 and 5 shots, in this case not even 10 shots accurately represented the gun/ammo. So does 20 shots? Yeah, pretty well. notice in the chart that there is no change in ES after the 14th shot. That doesn't mean there won't be a change if more shots are fired, but it's a pretty good indicator. This is kinda like our basketball player shooting 20 free throws - that shows a lot better what he can do than 3 tries would.

    Bear in mind, this is real data from my gun and load shot day before yesterday. I did no massaging of the data, and graphed it in the order it was shot. This is a completely random process.



    Since it is random, what if I had shot the rounds in reverse order? I mean just start at the other end. In the end, both the overall ES and SD have to be exactly the same as shooting in the actual order, but how they would get there could vary considerably. Here's a graph of the reverse order.



    These don't even look like the same loads do they? Notice we get to the maximum ES by the 8th shot and the ES is stable from there. That's because of where the high and low happened to occur within the group.

    The takeaway here is that the true excursions didn't occur within the first 3 or 5 shots. Again, just like 3 or 5 shots don't really represent the skill of a free throw shooter.

    A second point is that the SD can go up, down, or remain the same. The ES can only stay the same or go up - it cannot go down - ever!

    I'll include two more plots, one as shot and one in reverse order. All I'm going to say here is the max ES and SD occured at about the same place as before. But, it doesn't have to.It's quite possible the max ES and SD will be the very first two shots.

    These two look very similar whereas the two above looked distinctly different.





    While this only addresses ES and SD, the same principles apply to accuracy. You know that buddy with the expensive rig? He shot a 5 shot, 0.4 MOA group! Of course the next 4 groups were nowhere near that good. But, if he had shot that 0.4 group first and stopped, what would his mind be telling him about the accuracy of his gun? It'd tell him to it's a 0.4 MOA gun. But, when I got home and did an aggregate of his 5 groups, his overall accuracy was 1.25 MOA.

    Five shots just isn't enough.
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    Is he shooting the MDR chassis? I think that's the only one from Desert Tech that comes in 5.56, the rest are 6.5, 308, 50BMG, etc.
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    Quote Originally Posted by PPS1980 View Post
    Is he shooting the MDR chassis? I think that's the only one from Desert Tech that comes in 5.56, the rest are 6.5, 308, 50BMG, etc.
    He has a custom rifle built on the Desert Tech bullpup bolt action. I may have given Desert Tech a bit too much credit. He told me who builds the gun but I forget who he said.

    And, thanks for pointing that out.
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    The problem we have is people that want to kill large numbers innocent people
    in Gun Free Zones.

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    Quote Originally Posted by Tangle View Post
    He has a custom rifle built on the Desert Tech bullpup bolt action. I may have given Desert Tech a bit too much credit. He told me who builds the gun but I forget who he said.

    And, thanks for pointing that out.
    Just interested. They make some interesting long range weapons. Always interested in anything related to reaching out and touching someone.
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    Desert Tech
    https://deserttech.com/index.php
    Had to look into it Tangle.

    Due to something I read about the time I first got my chronograph in 1979 I've always been OCD and shot 10-shot strings. I never felt that I could take credit for a consistent hand load shooting five or less.
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    Quote Originally Posted by bmcgilvray View Post
    Desert Tech
    https://deserttech.com/index.php
    Had to look into it Tangle.

    Due to something I read about the time I first got my chronograph in 1979 I've always been OCD and shot 10-shot strings. I never felt that I could take credit for a consistent hand load shooting five or less.
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    Quote Originally Posted by bmcgilvray View Post
    Desert Tech
    https://deserttech.com/index.php
    Had to look into it Tangle.

    Due to something I read about the time I first got my chronograph in 1979 I've always been OCD and shot 10-shot strings. I never felt that I could take credit for a consistent hand load shooting five or less.
    I've never felt like I had a good handle on the load until I've run 30+ rounds through the chronograph.
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    If I'm seeing what I consider (and this is arbitrary) to be incongruities abounding then I might run an extra five shots while trying to judge if outside influences are affecting readings. If I haven't obtained satisfaction in 10-15 shots then I'm looking further into the hand load itself. It's probably not going to make the cut, especially if it's a serious rifle load. Now handgun loads or some low-power antique cartridges being used in old rifles with more primitive sighting equipment and at closer ranges, I may not take such pains, either with extra investigative chronograph testing or with the handloads themselves for that matter. After all, I'm not going to be using the .41 Long Colt in a revolver or the .32-20 or .38-40 in a rifle for precision at long range.
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    This is only my personal opinion which has formed my personal performance goals. If a rifle hand load is exhibiting over 50 feet-per-second extreme spread then I'm not happy and I like less than 40 fps extreme spread and standard deviation down into the teens. This isn't scientifically derived but rather what I've discovered to be do-able with my best hand loading efforts with sporting rifles and cartridges. I'm not shooting in competition at 600-plus yards and the only 600 yard competitive shooting I would contemplate would be high-power. It's been so long since I've shot at that distance that I'd stink and my rifles aren't match tuned anyway. For big game, I desire to be certain out to 300 yards with a scoped rifle of the .30-06 class.

    Oh, and I desire a maximum of one minute-of-angle to be happy with the rifles I take seriously, less with the varmint rifles is better.
    Last edited by bmcgilvray; August 22nd, 2019 at 08:32 AM.
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    Quote Originally Posted by bmcgilvray View Post
    This is only my personal opinion which has formed my personal performance goals. If a rifle hand load is exhibiting over 50 feet-per-second extreme spread then I'm not happy and I like less than 40 fps extreme spread and standard deviation down into the teens. This isn't scientifically derived but rather what I've discovered to be do-able with my best hand loading efforts with sporting rifles and cartridges. I'm not shooting in competition at 600-plus yards and the only 600 yard competitive shooting I would contemplate would be high-power. It's been so long since I've shot at that distance that I'd stink and my rifles aren't match tuned anyway. For big game, I desire to be certain out to 300 yards with a scoped rifle of the .30-06 class.

    Oh, and I desire a minimum of one minute-of-angle to be happy with the rifles I take seriously, less with the varmint rifles is better.
    That's me exactly! ES less than 50 fps, SD less around 15 fps, and I believe you meant a maximum of one minute-of-angle. Then for me 300 yard for predators and varmints with 223/556.
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    Yeah, I did mean a maximum of on minute-of-angle though a minimum might be more to the point of my grouping prowess.
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    I tend to use one-shot MOAs. It helps reduce the size. Saves ammo too.
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    Quote Originally Posted by OldVet View Post
    I tend to use one-shot MOAs. It helps reduce the size. Saves ammo too.
    You may be on to something there!
    We don't have a gun problem in the US, We have a people problem.
    The problem we have is people that want to kill large numbers innocent people
    in Gun Free Zones.

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    Quote Originally Posted by Tangle View Post
    You may be on to something there!
    I'm still grounded due to a home improvement project taking longer than expected (naturally). So a lot of Mongoose loads have been filled. However, I think I'll take my 788 .223 out next time to see what numbers come up with it. I know the IMR 4198 was terrible in the Mongoose, although it functioned fine in the Armalite AR.
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