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Ladder Test Results...need help analyzing.

 
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  #15  
Old 10-08-2012, 06:32 PM
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Join Date: Aug 2003
Location: NC, oceanfront
Posts: 3,262
Re: Ladder Test Results...need help analyzing.

You didn't resolve a single thing on my hit-list..
Something went wrong with your ladder before you even left for the range.
And the sentiment: ~used to hit steel at 700yds, means diddly about now.
Right?

So keep workin here:
- Your scope conceals .43" at 300yds(not exactly precision). Have you shot a box with it, and/or verified solid POA? Has the scope ever shot well?
- Go ahead and consider .001 off the lands the very worst seated condition -ever..
- You didn't address neck tension or headspacing..
- You didn't address firing pin strike..
- You didn't say your barrel and ammo temps were the same including 1st thru last shot in the ladder.
- "Front & rear rest" what were they?
- Are you still sure your gun shoots upside-down ladders?
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  #16  
Old 10-09-2012, 12:54 PM
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Re: Ladder Test Results...need help analyzing.

Those believing the OCW method is reality should learn that most rifle barrels whip the greatest angular amount at the muzzle around 400 to 500 cycles per second vertically. It's a harmonic of the fundamental or resonant fequency of the barrel which is a lower frequency. This is the main contributor to vertical shot stringing on target. That 18,000 fps speed of sound thing the OCW site dwells on only changes muzzle diameter a few millionths of an inch. If it was enough to see accuracy problems, then there would be no copper wash the last inch or so of the bore 'cause the bore and groove diameters would have opened up enough to be harmful. As long as that copper wash is there, bullets are well guided out the muzzle.

If the bullet not being touched by oversize diameters at the muzzle, then why do Garands rebuilt into precision match grade service rifles still shoot sub 2/3 MOA groups at 600 yards with the lands and grooves worn away from steel cleaning rods for the last inch or so of the bore back from the muzzle? All four of the Garand barrels I wore out did this.

It's best that bullets leave just before the muzzle axis is going up and reaches its highest angle so slower ones leave later and faster ones leave slower to compensate for their trajectory curves. It doesn't matter where that high frequency shock wave is. Even the best lapped precision barrels have more dimensional tolerances that what that shock wave creates.
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  #17  
Old 10-09-2012, 07:57 PM
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Join Date: Feb 2005
Posts: 564
Re: Ladder Test Results...need help analyzing.

Bart,

I have a high level of respect for you, and I do believe that you're saying what you feel is true.

However, I'm only the designer of the OCW system, engineer Chris Long (formerly of Boeing aircraft) is the one who gave the "why" as to why the OCW system works.

What we needed to understand was why a single match load recipe (the which you've shot tens of thousands of over the years, I realize ) could work so well in so many different rifles. There had to be something other than mere barrel harmonics at work here, since load recipes exist that seem to defy them.

And you of course know that there are many standard "go to" highpower recipes that thousands of shooters over the years have used in thousands of different rifles--and they shoot well.

The shock wave is a real factor on barrel behavior. In fact, it's the shock wave that initiates the vibrations... causing the muzzle to trace a repeatable pattern as the bullet is moving down the barrel. And that wave cycles back and forth from chamber to muzzle at the speed of sound in steel (about 18K fps).

In truth, the OCW simply is an improvement of what folks have attempted for years to glean from a "ladder test." Sometimes ladder tests work--and sometimes they don't (as we're seeing here). But a properly shot and interpreted OCW test will work every time it's tried.

I appreciate your having read my OCW pages, and even if you don't agree with me as to the "why" I hope you'll concur that this method has worked very well for over a dozen years, and literally thousands of handloaders use it now. If you google simply my first name (Dan) and "OCW", you'll see what I'm talking about. Not trying to boast... just wanting to point out that a faulty or nonsensical method for doing anything will wither on the vine if in reality it does not work.

Find me a guy who says OCW doesn't work... and I'll show you close to 100 folks who will strongly disagree with him.

But Bart... I'm still a fan of yours. I like these pages, where you have contributed much over the years--and much of what you say in this link is well worth folks taking the time to read... here's the link--> Guns

Dan Newberry
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  #18  
Old 10-10-2012, 07:06 AM
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Re: Ladder Test Results...need help analyzing.

Dan,

Has anyone measured bullet exit at the muzzle vs shock wave position to verify it works? Until that's been done, I'll consider the whole idea an interesting theory.

18,000 fps for the speed of sound in steel is only one of several claims for it. Others clock it as low as 13,000 fps. Which means, depending on the speed of sound in a stainless steel barrel, muzzle velocity of a 175-gr. bullet from a .308 Win and barrel length from 22 to 28 inches, there'll be from 6 to 11 round trips of that shock wave in the barrel before the bullet exits. I don't think the timing could be precice enough to make it work unless barrel time and muzzle velocity spread varied less than 1/5th percent.

Where does that shock wave start from? I don't thing that's been stated. If it's any place other than the head of the case, then there'll be two of them starting out in opposite directions.

Interesting reading:

Vibrations of Rifle Barrels : Mallock, A. : Free Download & Streaming : Internet Archive

Last edited by Bart B; 10-10-2012 at 10:00 AM.
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  #19  
Old 10-10-2012, 03:04 PM
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Location: Central AZ
Posts: 906
Re: Ladder Test Results...need help analyzing.

While this thread is an interesting read, I'm not sure it is helping jtkratzer with his initial problem of interpreting the data from targets. Perhaps a new thread is in order?

JT - have you had the opportunity to re-shoot your ladder, or tried the OCW method yet?
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  #20  
Old 10-10-2012, 03:17 PM
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Re: Ladder Test Results...need help analyzing.

JT, I'd just shoot five 5-shot groups with increasing charge weights of 1 grain starting with 41 of 4350. Use the load that shoots the smallest one and shoot a 10- or 15-shot test group with it. You'll see quickly if that load's close to the best one. Then try again with 1/2 grain heavier and 1/2 grain lighter for charge weight; you may improve it a bit, but not much.

Don't get concerned about muzzle velocity unless that's more important than all the bullets landing on target close together.
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