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kdbarker

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I was reading this from a post on AR Performance-Cartridges and found it interesting...

"10 Round Load Development Ladder Test - This is a load development approach he has refined to quickly identify accuracy nodes with only 10 rounds. Additional cartridges are then loaded to test and confirm these accuracy nodes."

http://www.65guys.com/10-round-load-development-ladder-test/





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BIGGDAWG

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Reply with quote  #2 
just read and watched that myself. hope it works with the ar too going to try it out.
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RangerJoe

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Reply with quote  #3 
Me too!
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wikster1983

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Reply with quote  #4 
Interesting, very interesting!
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Airaddict

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Reply with quote  #5 
I too saw this the other day. I mulled through my data of the last several ladders i tested with CFE BLK and found those "flat spots" in the velocities.

So i settled on a flat spot to test further and am gonna test COAL length now.

I also found some 1680....finally. So i loaded up a couple 3 shot ladders with the 90gn TNT & 85gn MPG to see what kind of performance this powder gives.

Its a very Interesting method he describes.
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Rifter

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Keith, did you read the comments I made about that video in that thread?  Like I said there, I'm not buying just ten rounds.  I've been working up loads for a very long time on all kinds of calibers, and it just isn't that easy.  He also claimed that the curve going flat was because of barrel harmonics, and I don't buy that either, especially if you take case head expansion and primer pocket stretching into account.

I'd like to hear your take on it.  Bruce, you too.

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Airaddict

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Reply with quote  #7 
Whats yalls take on the OCW method? I barely just had this method explained to me a little over a week ago.
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MBW36330

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I posted this information on A.R. performance cartridge and 6.8 SPC Facebook pages. I did it to share information and I don't claim any ownership. I have tried it (numerous times) and it works very well.

If you decide to try it and have questions about this technique, I'd be glad to pass on what I have learned while using it.

In this example of the test when graphed, you'll see a flat spot where there's only 4 fps variation in velocity, which correlates with a 4/10 of a grain difference in charge weight. In theory, you could load a 42.2 grain charge on a progressive press and still achieve single digit es/sd with that load.

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Dvalin

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Reply with quote  #9 
Thanks for posting this, sounds very interesting and I will give it a try, possibly today.

 Can anybody explane how harmonics can effect velocity? I can't wrap my head around that one? 
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BIGGDAWG

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Quote:
Originally Posted by Dvalin
Thanks for posting this, sounds very interesting and I will give it a try, possibly today.

 Can anybody explane how harmonics can effect velocity? I can't wrap my head around that one? 



if you read this article on obt it explains it well basically you are trying to get the bullet leaving the muzzle in the middle of a pressure wave

http://www.the-long-family.com/optimal%20barrel%20time.htm

there are charts that will tell you optimal barrel times for x length barrel which actually correlate to basically optimal velocities for each barrel length. i have used quick load to estimate barrel times and match up velocities to estimated barrel time and the nodes are pretty close most of the time.

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kdbarker

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Quote:
Originally Posted by Dvalin
Thanks for posting this, sounds very interesting and I will give it a try, possibly today.

 Can anybody explane how harmonics can effect velocity? I can't wrap my head around that one? 


Its not that barrel harmonics effect velocity, but rather velocity effecting barrel harmonics that we would be looking at here. You are looking for a barrel pressure point (velocity) that gives you a "flat spot" where the SD is low and velocity flattens out over a small range of powder charges.

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kdbarker

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Reply with quote  #12 
Quote:
Originally Posted by Rifter
Keith, did you read the comments I made about that video in that thread?  Like I said there, I'm not buying just ten rounds.  I've been working up loads for a very long time on all kinds of calibers, and it just isn't that easy.  He also claimed that the curve going flat was because of barrel harmonics, and I don't buy that either, especially if you take case head expansion and primer pocket stretching into account.

I'd like to hear your take on it.  Bruce, you too.


Rifter, I don't think this is meant to be an "end all" new standard for working up loads, but rather something of interest that may give us some interesting data. I always keep in mind the phrase "nothing is everything, but everything is something". No different here, and I am always open to experimenting with different processes to gather data points. Of course, as you mentioned, you have to practice good reloading techniques and standardized practices with quality components, proper case prep/inspection, etc...     

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JBFA

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Reply with quote  #13 
Quote:
Originally Posted by BIGGDAWG
just read and watched that myself. hope it works with the ar too going to try it out.


Man BIGGDAWG, that could potentially save you MILLIONS[biggrin]

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RIGGS68

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Reply with quote  #14 
Thank you for posting the video. During load development for Mongoose #1 I did notice flat spots in the ladder and they appeared to coincide with the same velocities regardless of the powders I used. My take on this is that the barrel harmonics resemble an under dampened signal, therefore, you should achieve a node each time the signal crosses the "x" axis. If you step your ladders in .5 increments you could completely miss the node. The challenge is getting the best powder to get to the highest node and maintain low ES/SD-but then we all know that!
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Rifter

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Reply with quote  #15 
Quote:
Originally Posted by MBW36330
I posted this information on A.R. performance cartridge and 6.8 SPC Facebook pages. I did it to share information and I don't claim any ownership. I have tried it (numerous times) and it works very well. It's funny to me though that Riffter was the first one to post to the thread, came off as being a subject matter expert, yet hadn't ever tried it. LOL If you decide to try it and have questions about this technique, I'd be glad to pass on what I have learned while using it. In this example of the test when graphed, you'll see a flat spot where there's only 4 fps variation in velocity, which correlates with a 4/10 of a grain difference in charge weight. In theory, you could load a 42.2 grain charge on a progressive press and still achieve single digit es/sd with that load.


That I commented first has nothing to do with one way or another.  My response was based what I read and watched, and my own experience doing load workup for a long time.  It boils down to the fact I don't think 10 rounds gives you enough information to make a good determination, and I'm more meticulous than that in general.  I know how the process works, so the fact I haven't tried it personally is not really the point.

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Dvalin

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Reply with quote  #16 
Quote:
Originally Posted by BIGGDAWG
if you read this article on obt it explains it well basically you are trying to get the bullet leaving the muzzle in the middle of a pressure wave

http://www.the-long-family.com/optimal%20barrel%20time.htm

there are charts that will tell you optimal barrel times for x length barrel which actually correlate to basically optimal velocities for each barrel length. i have used quick load to estimate barrel times and match up velocities to estimated barrel time and the nodes are pretty close most of the time.


 Sorry if I'm being a waterhead, but I guess I asked the wrong question. I'm trying to understand what is actually causing the flat spots in velocity, and why it's and indicator of a node?

 I did read the OBT paper (thank you) but I'm still not seeing how the timing of the pressure wave would flatten out the velocity?

Thanks for bearing with me!



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RangerJoe

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Reply with quote  #17 
See if this helps:

Incremental changes in propellant do not always produce matching changes in velocity.  For example, let's say your test ladder looked like this (made up numbers):
  1)  34.0gr = 2600 fps
  2)  34.2gr = 2630 fps
  3)  34.4gr = 2660 fps
  4)  34.6gr = 2695 fps
  5)  34.8gr = 2705 fps
  6)  35.0gr = 2699 fps
  7)  35.2gr = 2715 fps
  8)  35.4gr = 2760 fps with blown primer

You can see that the first few increments of 0.2gr charge increase produced fairly consistent increases in MV.  You could plot this on a graph... say MV on the Y-axis and Charge on the X-axis.   The curve would show a fairly steady slope.  Then suddenly, the MV "flattens out" and does not increase with similar increments as before. This is a "node".  In some cases, MV actually DECREASES with an increase in powder. 

Often when approaching max loads, the pressure (hence MV) spike WAY up with even a small increase in powder.  Cue Top Gun music... "Highway to the Danger Zone"

Since MV affects bullet trajectory - the more consistent the MV of multiple rounds, the more "likely" it is these bullets will fly in a similar fashion.  In the above example, selecting a charge weight of ~34.7gr would appear to be middle of the node.  If you charged one case at 34.6, another at 34.65, and a third at 34.75 - the MVs would be very close... hence the bullets would fly very similarly.

Finding a velocity node is NOT a GUARANTEE of optimum accuracy... but more often than not, it is pretty damn close (if not spot on).



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MBW36330

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Reply with quote  #18 
Quote:
Originally Posted by RangerJoe
See if this helps:

Incremental changes in propellant do not always produce matching changes in velocity.  For example, let's say your test ladder looked like this (made up numbers):
  1)  34.0gr = 2600 fps
  2)  34.2gr = 2630 fps
  3)  34.4gr = 2660 fps
  4)  34.6gr = 2695 fps
  5)  34.8gr = 2705 fps
  6)  35.0gr = 2699 fps
  7)  35.2gr = 2715 fps
  8)  35.4gr = 2760 fps with blown primer

You can see that the first few increments of 0.2gr charge increase produced fairly consistent increases in MV.  You could plot this on a graph... say MV on the Y-axis and Charge on the X-axis.   The curve would show a fairly steady slope.  Then suddenly, the MV "flattens out" and does not increase with similar increments as before. This is a "node".  In some cases, MV actually DECREASES with an increase in powder. 

Often when approaching max loads, the pressure (hence MV) spike WAY up with even a small increase in powder.  Cue Top Gun music... "Highway to the Danger Zone"

Since MV affects bullet trajectory - the more consistent the MV of multiple rounds, the more "likely" it is these bullets will fly in a similar fashion.  In the above example, selecting a charge weight of ~34.7gr would appear to be middle of the node.  If you charged one case at 34.6, another at 34.65, and a third at 34.75 - the MVs would be very close... hence the bullets would fly very similarly.

Finding a velocity node is NOT a GUARANTEE of optimum accuracy... but more often than not, it is pretty damn close (if not spot on).
Very well said Sir
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Dvalin

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Reply with quote  #19 
Quote:
Originally Posted by RangerJoe
See if this helps:



Ranger,
 Thanks for the great info, very well put. I do understand what has been said so far, but I'm still looking for the WHY of what physically happens to cause the velocity node to happen in the first place. 

Thanks again everybody!
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RangerJoe

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Reply with quote  #20 
Within the complex field of study we call ballistics, there are three "broad-brush" sub-fields:  Internal, External, and Terminal (there are actually even finer sub-sub fields):

Internal ballistics takes into account everything that happens until the projectile leaves the barrel.  External ballistics is the Newtonian-physics study of objects in motion (acceleration, drag, stability, gravity, lift, mass, velocity, time, etc.).  Terminal ballistics is the study of what happens (i.e., physics, biomechanics, and biomedical) when a projectile impacts a given target.

Of the three, External Ballistics is perhaps the best defined and easiest to visualize.  We have very exacting equations for how humidity, velocity, and altitude affect drag; or how to calculate the rotational stability of a typical bullet (i.e., without fins).

Internal ballistics has many components/variables such as rate of change of pressure, peak pressure, volume (case, propellant, chamber, barrel,) burn characteristics of the propellant, friction, inertia, expansion ratio, etc.; it is a bit harder to measure & visualize.  The interactions of all these non-linear variables results in sometimes little changes have LARGE effects, and/or seemingly larger changes yielding only minor effects.

Terminal ballistics has "variables" that can't always be measured or calculated.  Why does one person die when shot in the eye with a BB rifle and another survive having half their skull blown off? 


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Dvalin

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Reply with quote  #21 
I had some time to give this a theory a try. I fired 3 identical ladders to see if there was a consistent result. 
 There certainly seems to be a flat spot between 24.2-24.4gr. , but is that a good load? Needs more testing.....we'll see.
bfe66204-bb7d-4934-bd6a-d049ac101248.png 

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Airaddict

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Reply with quote  #22 
Thats a high speed low drag little plot chart. Looks like you can aim between those charges to get consistent velocity with that recipe. Good job! Wonder if seating depth will alter your numbers for better or worse now.
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