Home Forums Hunting & Shooting Ask The Gunwriters SD and ES

Caveat is that it depends on how I shoot those 3-5 round groups. Some times I put a target up and shoot 1 shot now and then over the course of a week. yes it tests the zero. But it also tests the accuracy.

Sometimes I overlay and measure.

But you dont' always have to have large numbers of shots all at once to confirm.

OTOH if I am shooting a 20 shot plus match, then I need to know what heat etc... does to the group as you get to 20.

In theory as I've noted, if I put out my 3 inch target at any distance from say zero to 600 yards like I do at home, and I rarely miss that, I'd say for a hunting load it proves the point well enough.

Granted a few 3 or 5 shot groups prove that you may or may not be homing in on a good load. A lot of those groups will confirm or deny.

Then there was old 00. I can't recall his name be we called him Double Ought. Heck of a shooter. Maybe thought too much about technical though. He weight sorted cases or maybe it was volume. Anyway his cases were always numbered. I have no clue anymore which way he fired them, but it was that as the gun got hot, the pressure, speed etc.. went up.. or was it that the barrel grew in size and it went down? I dont' recall his theory. Anyway the answer was to fire cases in order such that you either were building case capacity or not and that affected velocity to match whatever was happening as the match went on.....

I will and have admitted this. I generally dont' take the time to care WHY something is happening. I just want to know that its happening. And thats where my input gets a bit iffy. I can make it work well enough for my uses. For yours they may differ.

I am totally convinced though that having the most accurate consistent load out there negates variables and allows you to make more mistakes, and get away with them. And it also allows you to know that the mistakes are YOURS and not the equipment and I love it when I know its me and not the gun.

I have had some really wow moments like a tack driver 308 with an MTU contour 26 inch tube on it. Missed a standing still spike shot at about 310 yards. Sent for the head. Nothing happened. I should have stopped. So I shot for the lungs. Nothing happened. Did it the 3rd time. No results. We look for the deer after it ran off and found no sign of a hit. I had dialed the elevation. Found out at home the scope had died.... I should have realized that after the very first shot and stopped. But it taught me that lesson and it happened again some years later very similar around 450 yards and when the first shot missed I stopped. Somehow that gun was off zero ... scope was fine. Gun was just off.

5 shot group @ 100 ES 76



10 shot group @300 same load same day



The ES showed itself at the 300 mark but still not bad. While with tuning I cut the ES down to 30 which is ~60%, my groups didnt shrink 60%. 🤔

The notion that you need 30 samples comes from the fact that if you are doing the basic Z test (the one they start you out on in basic stats), you need about 30 samples to meet the assumption that you really know the long term mean of the process. This is also about the point where the T Test (which everybody uses) and the Z test (which practically nobody uses) merge and become the same. It has nothing to do with the sample size needed to estimate ES or SD.

Measures of dispersion, like range (which shooters call ES) and standard deviation are harder to pin down than estimates of means. For example, I just ran a simulation with 30 data with SD = 15, and the estimate of the mean was only reproducible to between about 11 and 18.5. You can get a good estimate of the mean with a smaller sample than an estimate of SD.

SD and ES can be converted from one to the other. For a sample of 5, divide your estimated ES by 2.3 to get an estimate of SD.

SD of MV usually matters very little, so long as it is something reasonable, say below about 35 FPS. Since variation does not add linearly, the total variation will be almost entirely governed by the largest source of variation, which is normally not MV.

Interesting. Thanks. This is neat.

I might be thinking about this wrong but hear me out.

ES of 75 - shoot a .75 MOA group
ES of 10 - shoot a 1 MOA group

Which one would I feel best about reliably repeating those group sizes over a period of time (assuming condition not a factor, 10mph wind or not etc) and assuming nothing else changes like powder lot, primer, seating depth etc.?

Does that variability in the ES75 group's ability to repeat actually matter? That is to say it might shoot a .75 or 1.25 due to ES but that's NBD if 2.0 MOA is good enough.

So the ES10 offers an "advantage" because it's more likely to continually print 1moa but the standard is 2moa - so who cares?

Probably thinking myself into a hole at this point lol.

The extreme spread and the standard deviation are not a measure of errors, they are a measure of normal distribution of a combination. We use past data points to predict the future.

You may say there are "errors" in our brass, bullets, powder, etc. No, an error is an unintended mistake. The variance in our components is the product of normal distribution. When we sort components, we are attempting to make a smaller, more consistent population by excluding the outliers. This, hopefully, results in more predictable velocity. Velocity will still have normal distribution, however the variability will be smaller and thus a smaller SD. We continue to measure things like seating force, neck tension, runout, and so on to cull errors.

Statistical analysis determines probability of an output using given inputs, based on previous data. The probability of outliers is the inverse of our confidence. After all, anything CAN happen. That doesn't mean it is likely. The larger the historical data sample, the more confidence we can have predicting the future.

Agreed - not looking to use ES/SD to predict a load as the most accurate, that it's likely to be the most repeatable. An accurate load that's not repeatable from string to string is what I'd be looking to avoid, using SD/ED as a measuring stick for that likelihood.

Basically, muzzle velocity variation only matters if the rifle and shooter are able to shoot the normal distribution (precision) at a range which velocity variation results in more drop than the rifle's level of precision.

If a rifle is a 1 MOA rifle, velocity variation won't be critical until the standard deviation could result in more than 1 MOA of drop variation.

So what do you think is a reasonable SD/ES for a 3000 FPS cartridge?

Follow Rost's advice & pay more attention to which loads are the most accurate on the target....................in the end that's what matters most.

MM

Two guys that “get it”

Another comment: The reason that major ammunition factory I mentioned uses a minimum of a 30-round SD is they're trying to make ammo that will tend to group well enough in a bunch of different rifles, mostly factory. And in my experience that works pretty well. Some of it has even averaged 1/2" or so for 3-shot groups in some factory rifles.

Of course, this ain't small enough for some more particular 21st-century hunters....

What creates the harmonics in any given barrel and can harmonics be affected or are they simply inherent in a piece of steel at X length? Unchanging.

Barrel bedding also affects harmonics--which is why one maker of very accurate rifles fully-bedded the barrels of his rifle in very stiff stocks. But even then groups would vary some with different loads....

Bud in a perfect world lowest ES/SD would win every damn time if all conditions were perfect, equipment even steven and there were no human interactions. It isnt a perfect world.

Good read here

https://www.angelfire.com/ma3/max357/houston.html

Excerpt

For the most part, shooters arrived at the warehouse with troubles. Their rifles were inconsistent — one group in the teens, the next in the .3’s — for reasons they could not fathom. Others had consistent .25" to .30- something rifles, an accuracy level guaranteed to put a competition shooter down near the bottom of the pack. With the list of potential problems significantly narrowed by the elimination of moving air and dancing heat waves, the answers were easier to isolate in the warehouse, and shooters drove hundreds of miles or flew into Houston to get to the source of their tribulations.


ES/SD had nothing to do with it.

Every thing can be expressed as a wave function, including your body, (one of the first calculations on any physical chemistry or wave equation finals). The question what type, standing, sinusoidal, Bessel. longitudinal, etc.They are called harmonics because of their standing wave characteristic, repeating nature, ( they are not harmonic by a math definition). Think of a drop of water hitting a pool. The first wave is a peak, then each surrounding one is a circular one with a diminishing amplitude. Bessel functions. They appear to be harmonic if the instrumentation used set up to detect other types of waves.

It really depends on what you're doing with it. For example, 100 FPS ES in a .308 Win shooting 175 gr GMM would result in about 8" of vertical at 600 yards. Combine that with 1 MOA shooting, you have a potential of 14" of vertical if you break your shot perfectly every single time. I wouldn't want to hunt with that load at that range. It would be unethical. Target shooting? Knock yourself out.

If you're hunting 300 yards and in, it would take an extreme example to make it have much effect.

That's because they weren't shooting far enough for ES/SD to matter.

This 1000 yard group with my Palma rifle gives a good visual of velocity variations showing as vertical on the target.

That's exactly right, when shooting my short range Benchrest rifle I very seldom get out the chronograph, when shooting my long range rifles working up a load my chronograph is always there

I haven't played with SD and barrel harmonics in centerfires but, I have in air rifles. Same principles. Seems to me that finding a node in an Audet/barrel harmonics test makes your rifle more forgiving of bigger SD's and tiny SD's make your rifle more forgiving of not being right in a harmonics node. Ammunition manufacturers can only play with SD since they're loading for everybody's rifle. The question then, is which gives you the most forgiveness or biggest benefit - tiny SD or harmonics node, since you really can't chase both. Watching the wet noodle videos of barrels during firing, I'd guess an Audet/barrel harmonics node is going to give you more benefit than a tiny SD and should be sought first. My question would be, after finding the harmonics node can you then chase SD to any appreciable extent? Is that what that Cortina guy was doing in the video with OAL?

Thanks for making me think on a Saturday morning!

Check into structured barrels if you are curious about solving the problem using SD and correlations with and I use the term loosely "harmonics". They are based on the principle that tubes have more structural rigidity than rods. They also have the benefit of better cooling and are substantially lighter that the same size "bull" barrel.
Also any videos of "noodles" are due to the "too slow" pixel rate in the video equipment, If you choose a smaller bifurcation interval it doesn't give the same modeling.