Standard Deviation (SD)

[bsumoba]

I was more wondering if you are more concerned about ES or SD when looking at your groups' points of impact, their shot placement on the target, not the velocities.

I chronograph a barrel at the beginning to see what kinds of speeds I get in general. I usually attach the MagnetoSpeed to the barrel when "breaking in" a barrel. This tells me generally where the speeds are. Kills two birds with one stone and I do not put unnecessary rounds down the barrel.

Then, I do load development with no chronograph. I never once bring out the chronograph when I am at this step. So, to answer your question, no.

After I find a load that shoots well, then I chronograph. ES/SD typically ends up being where I want it to be.

If you use something like a LabRadar, then you could do this in parallel to load development, but I think people can overthink things when looking at speeds and groups at the same time.

[blockfort]

I mean the extreme spread and standard deviation of your group's actual placement on the target, not their speeds. What do you use to characterize your group's "size" and the accuracy of your rifle?

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[bsumoba]

I mean the extreme spread and standard deviation of your group's actual placement on the target, not their speeds. What do you use to characterize your group's "size" and the accuracy of your rifle?

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I saw your other post and I think I know what you are now asking and I am assuming you are wondering if low ES/SD is an attribute of small groups. In general yes. But, you can get away with a high ES/SD at shorter distances. A high ES/SD will really hurt you as you go further out in distance.

I will respond to your other post as well.

[ar15barrels]

What do you use to characterize your group's "size" and the accuracy of your rifle?

Calipers.

[blockfort]

Calipers.

I didn't ask how you stop your car.

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[ar15barrels]

I didn't ask how you stop your car.

I have never used these to stop my car:

[mjmagee67]

This is one of the funniest threads I've read in a while.

Taste great........less filling.

[LynnJr]

Blokfort
Standard deviation is a guess of how your ammo should shoot if you were to fire many dozens of rounds.
Extreme Spread is what your gun actually shoots for each individual group.

If you flip a coin 1 million times you should get 500000 heads and 500000 tails. This would be standard deviation.

If you flip the same coin 20 times and 19 times you get heads and only 1 time you get tails this would be Extreme spread or what you actually got and not a predictor of 1 million flips.

I dont care what my average group size will be over the next 5000 rounds I want to know what my chances of winning are over the next 20 shots.

[blockfort]

High SD, Low ES: 20 shots spread evenly around the 9, and 10 rings

Low SD, High ES: 19 shots in the X ring, 1 shot in the 8

[Unretarded]

Any reasoning you can share? The ES of one group is that group's "size", but the SD is a better predictor of future groupings and the total dispersement.

SD is a prediction....
ES is what is actually happening.


In simple terms, the weather man uses SD as a model.
When you open the front door and look outside and see what is taking place.....that is ES.

[Unretarded]

Custom barrels shoot so much more accurately that flyers are always caused by the shooter.
The goal of ladder testing is to find the node (which will usually be 3-4 rounds) with fewer rounds down the barrel.
It's OK if there is a flyer.
The pattern will still be evident.

It should be noted that 100yd group shooting is of very little use when seeking a load with lower horizontal dispersion at long range.
A long range ladder test is by-far the easiest method.
I have done several 600 and 800yd ladder tests as they get easier to read the further away you do them.
Two ladder tests with matching results assures that you are in the right spot.

This is very true^^^^^^^

I am not even shooting the long range test loads over a chrono or at 100 yards anymore.......pretty much a waste of time at this point.

The range I shoot at has a nice 12 inch target at 1000 yards with fine powder dirt above and below it......I just ignore wind drift and shooter error........

Out of the few powders and loads that seem to be doing the best, when shot at 100 yards look terrible........well not terrible, but bad enuff one might consider not shooting them at distance.


I guess I am using the chrono to check my reloading skills, rather than to develope a load.

[LynnJr]

High SD, Low ES: 20 shots spread evenly around the 9, and 10 rings

Low SD, High ES: 19 shots in the X ring, 1 shot in the 8

You will rarely if ever see low Extreme Spread coupled with a high Standard Deviation
In field conditions using a LabRadar my 338 SnipeTac was getting an extreme spread of 12 fps and my 50 BMG was right at 18 fps.
I don't know how much built in error the LabRadar has but my Oehler runs 2 fps at 3100 fps.

[blockfort]

You will rarely if ever see low Extreme Spread coupled with a high Standard Deviation
In field conditions using a LabRadar my 338 SnipeTac was getting and extreme spread of 12 fps and my 50 BMG was right at 18 fps.
I don't know how much built in error the LabRadar has but my Oehler runs 2 fps at 3100 fps.

Not talking about speed, I'm talking about the ES and SD of the POI of the shots compared to the POA.

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[LynnJr]

Blokfort
That is what I am talking about as well.
If your shooting F-Class where you shoot 20 shots that are spotted between each shot from the pits standard Deviation will unreliably predict where your rounds would hit but only with many many 20 shot groups.
With extreme spread you can predict your minimum grouping capability.
Naturally conditions and the distance you are shooting at will all influence the outcome.

Edit: You also need to consider the bullet used and the velocity it is fired at. Given 1000 yards.
A 308 Winchester with the same extreme spread as a 338 Lapua will group 7 inches larger at that same distance.