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  #21  
Old 02-23-2017, 09:41 AM
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Quote:
Originally Posted by unclenick View Post
"Before 1925, everybody divided by n, but, then, {Fisher} came out with his book on ANOVA. n-1 makes the math in ANOVA work cleanly, and the influence of ANOVA on the science of statistics was profound. After 1925, the world pretty much switched to n-1. The choice of n or n-1 is simply a matter of convenience, anyway, and does not spring from some great, secret truth, known only to statisticians."
Perhaps by making the math work "cleanly", he was referring to removing some degree of bias, and I realize I don't actually know. From the article I linked to, it clearly doesn't do a perfect job of that.
70 step proof: https://economictheoryblog.com/2012/06/28/latexlatexs2/

21 step proof: https://mycourses.aalto.fi/pluginfil...20Unbiased.pdf

Another Source similar to 'perverse', but highly mathematical: Statistical Measures of Accuracy for Riflemen and Missile Engineers, Grubbs
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  #22  
Old 02-23-2017, 11:09 AM
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The 3% figure for node separation comes from Dan Newberry. This is the figure he uses and I have used it successfully. This comes from his experience working with load development in many different firearms. I am not trying to say that this figure is etched in stone for every application, but it will get you very close when using the data obtained from a good OCW test.

As to statistical data from stings during development, data from 3 rounds is not statistically sound. It is ok to compare 3 shot strings using the data generated. Since I shoot the OCW round robin, I put the velocity data into a spreadsheet to calculate the statistical data. Even then, I will believe my target over the chronograph every time. If I have 2 or 3 groups that are sub 1/2 moa and are at nearly the same point of impact, I know that is my node even though the chronograph data may not support that. Once I start using that particular load, I will start collecting chronograph data for the next several range sessions. I will save those targets too. This allows me to build a much large sample population for really knowing that load. It is also a good way to check the consistency of your hand loading procedures.

My main reason for using a chronograph during development is to watch for excessive MV, which is the first sign that pressure is getting too high

Dennis
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  #23  
Old 02-27-2017, 07:51 AM
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F2G1D,

Thanks for the proofs. They are easy to follow, and the link in the first one to his 14 step short version is easier, still. I'm still hoping Denton will chime in.


Dsculley,

While an unexpected increase in velocity can occur with some powders as they are overloaded (a compressed load of Trail Boss, for example), the opposite is more common in working up rifle loads. As long as you are inside the normal pressure and load range for a cartridge, velocity and charge weight have a very linear relationship. However, when the pressure gets high enough, it can start stretching the steel to a degree that affects the peak pressure more than normal random variation does. The extra volume spoils the linearity, so the added powder actually fails to achieve the velocity predicted by a straight line graph. In extreme cases, the velocity goes down with the increase in charge due to the non-linear interaction of powder with peak pressure as affected by volume. You may know all this already, but for lurkers, in particular, I want to point out that either unexpectedly high or unexpectedly low velocities are pressure signs as you take a gun an powder charge towoard its safe limits.

The 3% separation does not match my experience very well. It also doesn't match Long's OBT numbers, as his model produces nodes that are alternately closer together and further apart. So you wouldn't expect a uniform charge weight difference to bridge them. I've had nodes wider than that (one in .308 Win with the 155 grain SMK over Brigadier 3032 that went from 40.5 to 43.0 grains), or 6% of the high number. Newberry himself has documented single nodes almost 5% wide (see his plus or minus a grain comment in the context of the .243 Winchester in his "example" page).

After I thought about it, I realized that I mispoke in my previous post and that Chris Long had told me of a 2% node spread. Rather, he said feedback had suggested his system used with tweaked QuickLOAD settings predicted nodes within about 2% accuracy, a single exception being a rifle he'd built using class A threads in the action and barrel, which got the metal intimate enough that the action became an extension of the barrel length. I'm wondering if node prediction precision is how Newberry is currently using 3%? A link to what he says about it would be useful.

Based on Long's theory, which Newberry references in his opening page and subscribes to, AFAIK, here's an example from QuickLOAD for a .308 Win load. The average charge between nodes is 7% for all the barrel lengths, but individual percent change (in blue text) is unevenly spaced because of the node timing spacing differing:

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OCW Testing-obt-powder-charge.jpg  
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  #24  
Old 02-27-2017, 10:17 AM
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Quote:
Originally Posted by unclenick View Post
F2G1D,

Thanks for the proofs. They are easy to follow, and the link in the first one to his 14 step short version is easier, still. I'm still hoping Denton will chime in.
... the peculiar properties which make the first two powers especially appropriate ... Statistical Methods for Research Workers, Fisher, 1925, p.46.

Although he offers some mathematical evidence in support of (n - 1), it is nothing like the previous proofs.
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  #25  
Old 03-08-2017, 10:13 AM
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Load Development



I did some load development today with a rifle , a Savage 12 .308, I received back from the gunsmith. I shot them all at .020" off the lands. However I applied the larger increments theory to the charge load. Instead of the usually .3 grain increments, I increased them to .5 grains. As seen the nodes are easily identifiable. I have a low node a 43.0 to 44.0 and a high node from 46 to 46.5 grains. I want to develop the high node, since I need the velocity for longer distances. I haven't decided whether to bracket the high node with .3 grain testing or move on to muzzle velocity testing. Interesting day; the wind was blowing 17mph with gusts to 38mph. I left before noon, but my buddy stayed to face 27mph winds with gusts to 49mph.
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  #26  
Old 03-08-2017, 02:43 PM
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I think I would bracket the high nodes starting at 45.8 in .3 grain steps to 46.7 to see if I could make the width and center of the node more clear. Then get velocities across the range so you can check them under different temperature conditions. With luck, the middle of your range will stay good across the range of conditions you shoot in. Right now it looks like about 6% charge difference between your nodes.

I would drop back to the wider node that appears to be at 43.5 grains for the purpose of testing different seating depths. Both its width and lower charge weight are going to be helpful to ignoring the pressure changes involved in moving the bullet around.
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  #27  
Old 03-08-2017, 04:42 PM
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Wow! What is OCW, please?
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  #28  
Old 03-08-2017, 05:53 PM
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Optimal Charge Weight. Dan Newberry's formula for finding the best load and "node" where the barrel harmonics are optimized. (Layman's explanation. Experts can correct, edit, and clarify)
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  #29  
Old 03-08-2017, 05:56 PM
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Thank you! In two pages of post it was never said and I've never heard of it by than name.
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  #30  
Old 03-09-2017, 08:22 AM
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Ahh! Sorry. It's one of those things that's been around for awhile so I sometimes forget to define it. Newberry's idea is that some loads exist that seem to work well in a lot of rifles and barrel lengths (the Federal Gold Medal Match with 168 Grain Sierra MatchKing is his example), and he wanted to develop a system for identifying such loads. He calls them chocolate ice cream loads on the premise that rifles like these loads the same way people pretty universally like chocolate ice cream. He decided the Audette ladder was too limited in that it only took the vertical axis into account and that you need at least 200 if not 300 yards to resolve it adequately. Unlike the Audette ladder, which uses just one shot at each load level, the OCW use three, looking not for just a stall in vertical POI, but a common center that doesn't move for several small load increments. I've found it works pretty well and can be used at 100 yards without resolution confusion.

As with any other kind of accuracy workup, if you have a gun with problems caused by it being badly in need of bedding, its lugs need lapping, its barrel needs recrowning or perhaps to be floated, or the receiver has flaws that require blueprinting to fix, you may not get any sweet spots to identify. But that applies to any method of tuning.

Newberry's pages start here.
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  #31  
Old 03-19-2017, 05:32 PM
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.020 Seating Depth Jump

Tried .080, .060, .040, .020, and .000 at the 43.5 gr node. The load likes .060 seating off the lands. I had read the Bergers' comments on seating depths a while back, and in error had discounted it. Today's target says its the real deal!
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  #32  
Old 03-20-2017, 05:14 AM
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And now that you found that, you can try upping and lowering the load by a couple of 0.3 grain steps to make sure you're still in the middle of the tightest node for the seating depth. This stuff is interactive. I note that your 46.1 grain load at 0.040 off the lands produced a good group of 5, too. It makes me wonder if you went between the two, at 0.050", if you might find that will a step or two of 0.3 grain adjustment for each load, they might not both do well at that same seating depth.
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  #33  
Old 03-20-2017, 04:16 PM
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Nick, The nine targets are confusing. The first five are 43.5 gr at .080, .060, .040, .020, and .000 seating depth. The next four targets are .020 seating depth at 45.8, 46.1, 46.4, and 46.7 grains. I was trying to flush out the width of the high node.

That was the last of my Sierra 2155 bullets, and I've decided to move on to a bullet with a better BC. With the new bullet load development you can bet I will use this scheme when it comes to seating depth. Thanks, Brant
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  #34  
Old 03-22-2017, 10:26 AM
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It is interesting to note that the two charges mentioned, 43.5 & 46.1 are two 3% steps apart.
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Old 03-22-2017, 10:53 AM
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AND that there is an .040" seating depth difference between the two
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