Standard Deviation (SD)

[ar15barrels]

I think the theory is that as you approach nodes, the velocities will flatten out somewhat at the nodes.

That's not how it works.
The bullet velocity tracks with pressure.
What you are doing when you search for a node is searching for the TIMING of when the bullet leaves the barrel within the barrel's range of movement.
The accuracy node will be found at the top or bottom of the barrel's swing where the BARREL is moving the slowest.
Since the barrel is moving the slowest, you get a wider RANGE of powder charges with a smaller horizontal displacement on target.

If you could instrument the BARREL's movement and the bullet's release from the barrel, you could determine the optimum powder charge more reliably than a ladder test.

[Thoughts]

And yes adding more shots makes your junk ammo look better than it truly is.

How so?

[bsumoba]

That's not how it works.
The bullet velocity tracks with pressure.
What you are doing when you search for a node is searching for the TIMING of when the bullet leaves the barrel within the barrel's range of movement.
The accuracy node will be found at the top or bottom of the barrel's swing where the BARREL is moving the slowest.
Since the barrel is moving the slowest, you get a wider RANGE of powder charges with a smaller horizontal displacement on target.

If you could instrument the BARREL's movement and the bullet's release from the barrel, you could determine the optimum powder charge more reliably than a ladder test.

Not arguing Randall. I am in complete agreement with you. I have never done this. While breaking in a barrel or in the very early stages of load development, I will chronograph 1 shot of each charge to get an idea of the velocity. After this, the chronograph doesn't come out until after I develop a load. The velocity is what it is. I have learned that velocity is worth nothing if it can't consistently shoot well at distance.

[Metal God]

How much do you think your hold on the rifle effects ES/SD ? I did a limited test a couple years ago and would like to hear some thoughts on what you all think the effect has ?

[Rizzo]

What do you expect to learn from that?

The purpose of a ladder test is to find the barrel's charge weight node.
Then after that, you adjust seating length to fine tune the accuracy within the node.

Then you can dig out the chrono to check the ES/SD and see what you have...
Velocity measurements during a ladder test will NOT give you SD or ES figures of any use.

Using a chrono for my ladder tests (in my mind) gives me an idea of how hot my loads are. Especially if I am using a new bullet that I cast.
By using the load manuals for reference I can see if my fps results are close to published results in the manuals. i do check for pressure signs on the case also.

Ultimately it is how tight the target spread is that helps me to determine which load is working best for that firearm, assuming I am not bordering overpressure. I also notice the ES to check my loading consistency.

You make some good points. Thanks, and thanks to everyone that has replied to my SD question. I continue to learn in this fun hobby.

[ar15barrels]

Using a chrono for my ladder tests (in my mind) gives me an idea of how hot my loads are. Especially if I am using a new bullet that I cast.
By using the load manuals for reference I can see if my fps results are close to published results in the manuals.

That's the perfect reason to use a chronograph during the ladder test.
In case you are mis-using the term "ladder test", a ladder test is a sequence of shots with incrementally increasing powder charges that are fired at a target while using the exact same aiming point for the whole sequence.
The velocities will increase with each increase in powder so that the shots tend to "climb a ladder" on the target.

SD and ES only come into play when you are firing multiple shots of the SAME powder charge though.
You should completely ignore the SD and ES during a ladder test.

[JMP]

I agree with the guys that value the range (ES) over the SD. For me, standard deviation has never made much intuitive sense from an ammo perspective. The lower SD will, however, result in more "lucky" small groups over a long period of time. As it is the worst shot that defines your accuracy that is more valuable to me. Keep in mind that a low ES implies a low SD. As the ES goes to zero, so does the SD.

Really, SD doesn't mean beans unless you are working with large result sets that can be normalized. I believe that the reason that an SD is measured are for the ammo makers that test thousands of rounds as it becomes helpful in analysis with a lot of data.

Stats guys use standard deviation, and math guys use the square root of the variance.

[LynnJr]

When your performing a ladder Test your chronograph numbers will look like a sine wave. As you approach a node your velocity change per grain of powder will lessen and as you leave a node it will widen.

As you incrementally increase your powder charge your barrel will whip up and down. Your best accuracy will be closest to the top of an upward swing. Your worst accuracy will be seen when your barrel is swinging in a downward motion.
The reason you want the barrels muzzle climbing is that it takes longer for slower rounds to reach the muzzle. Slower rounds exit at a higher muzzle angle than do faster rounds and converge on the target.
If your barrel is dropping or on a downward swing the slower rounds will exit at a lower muzzle angle and the two rounds will never converge.
Some believe that while chronographing you will get slower rounds to hit higher at extended ranges and this is a myth. If your shooting a railgun or unlimited heavygun your higher velocity rounds will always impact higher on the target.
Here is a 5 shot group shot at the PacRat Invitational using such a gun. The Shooter was a 16 year old kid. The spot below the group is a single pen mark and the group is right at 0.120 inches.

[bsumoba]

When your performing a ladder Test your chronograph numbers will look like a sine wave. As you approach a node your velocity change per grain of powder will lessen and as you leave a node it will widen.

As you incrementally increase your powder charge your barrel will whip up and down. Your best accuracy will be closest to the top of an upward swing. Your worst accuracy will be seen when your barrel is swinging in a downward motion.
The reason you want the barrels muzzle climbing is that it takes longer for slower rounds to reach the muzzle. Slower rounds exit at a higher muzzle angle than do faster rounds and converge on the target.
If your barrel is dropping or on a downward swing the slower rounds will exit at a lower muzzle angle and the two rounds will never converge.
Some believe that while chronographing you will get slower rounds to hit higher at extended ranges and this is a myth. If your shooting a railgun or unlimited heavygun your higher velocity rounds will always impact higher on the target.
Here is a 5 shot group shot at the PacRat Invitational using such a gun. The Shooter was a 16 year old kid. The spot below the group is a single pen mark and the group is right at 0.120 inches.

So Lynn, how do you determine if you are on a node that is on the upward part of the swing and what if you found out your node is on the bottom end of the wave?

[LynnJr]

Bryan
If your node is near the top of the swing your slower shots will stay in the group as they will converge.
You can back a couple shots off 0.3 grains and they should not open up your groups.
The bigger the case volume the wider the node.
Your 6Dasher will only shoot tight for half a grain but your 7Shehane will shoot tight for 1.6 grains and your 338 Edge will shoot tight for 3 grains.

That said best accuracy will almost always be found closest to the top end of the node.
If your going to shoot locally and you develop your load in the same weather you can push the upper edge.
If your travelling and shooting in all kinds of weather you are best served by loading towards the center of a node.
The group above was shot from a 300 WSM using 187 BIB flatbased bullets and 66 grains of H4350 and my reamer has 0.287 freebore.
The node runs from 64-66 grains so it was right on the upper edge.
If I was going to shoot it in Colorado Montana or Pennsylvania I would use 64.5 grains and give up a small amount of velocity to make sure the gun was consistent and reliable.

[bsumoba]

Bryan
If your node is near the top of the swing your slower shots will stay in the group as they will converge.
You can back a couple shots off 0.3 grains and they should not open up your groups.
The bigger the case volume the wider the node.
Your 6Dasher will only shoot tight for half a grain but your 7Shehane will shoot tight for 1.6 grains and your 338 Edge will shoot tight for 3 grains.

That said best accuracy will almost always be found closest to the top end of the node.
If your going to shoot locally and you develop your load in the same weather you can push the upper edge.
If your travelling and shooting in all kinds of weather you are best served by loading towards the center of a node.
The group above was shot from a 300 WSM using 187 BIB flatbased bullets and 66 grains of H4350 and my reamer has 0.287 freebore.
The node runs from 64-66 grains so it was right on the upper edge.
If I was going to shoot it in Colorado Montana or Pennsylvania I would use 64.5 grains and give up a small amount of velocity to make sure the gun was consistent and reliable.

Makes sense.

When doing my initial load development, I will shoot in 0.2gr increments for the dasher and 0.3gr increments for the 7shehane. What I found in the barrels that are shooting well is that there was a range of powder charges that shot into essentially a big hole.

In my case, 33.2-33.4-33.6 varget shot into essentially one hole for the 6dasher and 54.6-54.9-55.2 h4831sc shot into a big hole for the 7shehane. My tuned load ended up being 33.5 for the dasher and 54.8 for the 7shehane.

[Metal God]

I was hoping at least one of you guys would have had an opinion on how one holds the rifle can effect velocity , ES & SD . For benchresters It's not likely as big an issue do to how much hold and actual interaction they have while firing . When shooting service rifle or guys that shoot in the field from field positions and need first round hits at unknown distances a consistent hold on the rifle is very important .

I did some limited test on this a couple years ago when I was having issues with my first shot being slower then the rest of the string . I was actually at the range and doing a semi live chat on another forum while I was there . I was there testing my velocity of a load I had found to shoot quite well . I knew that load was very consistent and was using it to find out why my first shot in my strings were 30-ish fps slower then the rest of the string . I was updating the thread after each string and applying and or trying the suggestions I was getting back from the posters in real time .

BartB was one of the posters helping me at the time . He suggested The consistency of how I hold the rifle can effect the velocity from shot to shot . Now I had heard him and others say this could be an issue but never gave it any real thought . Sure I thought about it before but really , how much could my hold really effect the velocity of my ammo . Well this time when I was reminded of it I was at the range with a very nice load I had developed . Why not give it a try and test it out .

Unfortunately I was at the end of my rounds I brought and only had 10 left to shoot . So I did two 5 shot strings starting each string with the same barrel temp and shooting each shot at the same intervals loading one shot at a time .

Rifle & load
308 Savage model 10 with heavy 24" barrel shot from a bench with front and rear bags
40.7gr IMR 4895 / 175gr smk / WLR primer / WCC-06 cases

Keep in mind all these rounds were loaded at the same time with all the same lot components and all were handle from my reloading bench to the rifle in the same manner

First string was shot with the rifle pulled in hard and tight to my shoulder for each shot .
Results = 2517 / 2582 / 2568 / 2552 / 2568 / ES-65.52 / SD-28.60

20min later with a cooled barrel I shot the second 5 shot string . This time I barely even touched the rifle and let it freely recoil for the most part . I did have to keep in control of the rifle but in comparison to the hard tight hold it was like not even touching the rifle .

Results = 2551 / 2555 / 2559 / 2552 / 2565 / ES-14.50 / SD-5.74

Remember same load , same rifle , same conditions . Only difference , how I held the rifle .

As you can see the first shot on the hard ,tight hold was slower then the rest . More then the 30fps I had been getting but I also had never held the rifle that tight before .

I believe this test and my subsequent test on other loads shows there is a direct correlation to how you hold the rifle and what your ES/SD will be .

[Rizzo]

That's the perfect reason to use a chronograph during the ladder test.
In case you are mis-using the term "ladder test", a ladder test is a sequence of shots with incrementally increasing powder charges that are fired at a target while using the exact same aiming point for the whole sequence.
The velocities will increase with each increase in powder so that the shots tend to "climb a ladder" on the target.

SD and ES only come into play when you are firing multiple shots of the SAME powder charge though.
You should completely ignore the SD and ES during a ladder test.

Yes, I was mis-using the term Ladder Test. Thanks for explaining that.

I guess what I really am doing is Load Testing.
I load up usually 10 rounds of each load, with powder measured manually for each round and using the same COAL. Generally each handgun load has .2 grain difference covering the spread of the suggestions in the load manuals.

So, I shoot 10 rounds of the same load from a benchrest, document the chrono results, check the cases for pressure signs, then I put up another target and shoot the next batch that is .2 grains hotter then repeat.

Then, I look at the chrono data and targets to determine which load has the best grouping on the target and verify the FPS from the manuals.

[ar15barrels]

Yes, I was mis-using the term Ladder Test. Thanks for explaining that.

In ladder testing, you load up 15-20 rounds TOTAL in very small powder charge increments to cover the whole charge RANGE from minimum to maximum.
Then, you setup a target at 300-400 yards and fire the whole string from lightest to heaviest, stopping after each shot to label the individual bullet holes on the target.
What you will find is that there will be a definite range where several rounds are very close in the vertical "climbing the ladder" compared to all the other shots which will have wider spacing on target between shots.



That tight sweet spot is where you want to be as it will give you the smallest groups at longrange.
You can also chronograph during ladder testing as well as look for pressure signs on each charge level.
That's usually how you know to STOP firing the ladder test.

[pacrat]

MG said

Remember same load , same rifle , same conditions . Only difference , how I held the rifle .

I find your test very interesting. The vertical stringing experienced due to variations in shoulder pressure was explained to me long long ago by Dean Grennell at a rifle range in OC.

"Recoil force is exerted in two ways. BACK, because of the Newton thing. And RISE, because the bore is above the stock. The less a rifle is allowed to move BACK during recoil. More of the force is diverted to muzzle rise." [paraphrasing of course, 40yrs and don't recall exact words]

{THEORY} Since your "hard held" velocities are measurably higher than a loose hold. Maybe there was a third reason that Dean never considered? Using the plasma energy generated by [X] grains of a given powder burning within the rifle as a constant in identical loads.

Understanding that pressure acts in all directions simultaneously. If you restrain the rearward recoil movement of the rifle.
That could concievably mean that the energy that previously acted on the movement of rifle, is then acting on the base of the bullet.

Just a thought.