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Rifles, Reloading, Optics, Equipment
Reloading
NODES _ Ladder test
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<blockquote data-quote="flashhole" data-source="post: 1164701" data-attributes="member: 21375"><p><a href="http://optimalchargeweight.embarqspace.com/" target="_blank">OCW Overview - Dan Newberry's OCW Load Development System</a></p><p></p><p>WHAT IS AN OPTIMAL CHARGE WEIGHT</p><p>LOAD?</p><p></p><p>With any given bullet and powder combination, there</p><p>will be a specific amount of that powder which will</p><p>cause the bullet to exit the muzzle at the "friendliest"</p><p>portion of the vibration cycle. This does not necessarily</p><p>correspond with the tightest velocity figures, however.</p><p></p><p>Many load recipes have over the years become the "go</p><p>to" recipes for trying out a new rifle. If your rifle fails to</p><p>shoot one of these "tried and true" recipes well, you may</p><p>well have a rifle integrity problem.</p><p></p><p>Consider the Federal Gold Medal Match .308 win ammo.</p><p>How can one recipe shoot so well in so many rifles? </p><p>That's what we're after in the OCW load--a load recipe so </p><p>stable and predictable that it does indeed rise above, </p><p>and to some extent disprove the "all rifles are different" adage of lore...</p><p></p><p>Think about it this way. Some kids like mashed potatos, some don't. Some kids will eat thier peas, some won't. Some kids like bananas, some hate 'em. But show me a kid that doesn't like*chocolate ice cream*and I'll show you one bizarre little character!*<img src="data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7" class="smilie smilie--sprite smilie--sprite1" alt=":)" title="Smile :)" loading="lazy" data-shortname=":)" /> An OCW load is like chocolate ice cream to your rifle. If your rifle doesn't like the recipe, there is likely something weird about your rifle.</p><p></p><p>If you perform the OCW load development properly,</p><p>you are not (in the initial stages) seeking the optimal</p><p>load for the test rifle. Heresy? Not really. There are</p><p>many known "universal recipes" that work well in most</p><p>rifles chambered for them. Ken Waters has made a pretty</p><p>penny with his book "Pet Loads" on this concept. Many</p><p>of the Waters loads have worked beautifully in my rifles,</p><p>and acquaintances have had the same experience.</p><p>Federal's Gold Medal Match .308 loads do well in</p><p>practically any .308 not needing a gunsmith's attention.</p><p>How can this be? If you subscribe to the philosophy that</p><p>"all rifles are different," and therefore need individual</p><p>loads tailored to accommodate their idiosyncrasies, how</p><p>do you explain the near universal MOA performance of</p><p>loads such as the Federal GMM? Universally good</p><p>recipes do exist. Upon realizing this, my questions have</p><p>been "How do such recipes work?" and "How can I</p><p>develop such a load?" </p><p></p><p>Recent conversations with very learned mechanical</p><p>engineers are affording me some better understanding of</p><p>just why an OCW load works so well in the majority of</p><p>rifles chambered for the cartridge at hand.</p><p>Here are some of the major points coming to light:</p><p>Uniformity of velocity (meaning low extreme spreads of</p><p>velocity) are definitely not*an indicator of the OCW</p><p>zone. We are actually finding that in many cases the</p><p>OCW zone does not have the tightest numbers--at least</p><p>initially. Fine tuning of the recipe with seating depth</p><p>variations and primer changes will improve the velocity</p><p>consistency, but simply shooting a succession of</p><p>graduated charges over the chronograph and looking for</p><p>a tight velocity spread will not lead you to the OCW. </p><p></p><p>As the reader comes to understand more about the main</p><p>shock wave (link Chris Long's pages elsewhere in this </p><p>webpage) it will become easier to understand how</p><p>bullets with larger extreme spreads in velocity can still</p><p>group tight (at closer ranges), while bullets with</p><p>seemingly tiny extreme spreads may group poorly. You</p><p>can tighten the extreme spread to improve long range</p><p>accuracy AFTER you identify the OCW.</p><p></p><p>Engineer Chris Long's model of barrel </p><p>behavior suggests (simply put, and in part) </p><p>that the initial shock wave, generated by the powder</p><p>charge's ignition, travels at the speed of sound in</p><p>steel (about 18.000 fps) from the chamber to the muzzle, then back, in a repeated pattern. When this wave is present at the muzzle, there is</p><p>naturally much turbulence and obturation of the</p><p>"roundness" of the bore at the muzzle. However, when</p><p>this main shock wave has reverberated back to the</p><p>chamber end, the muzzle is relatively stable. This</p><p>window of opportunity, according to Chris, is the best</p><p>time for the bullet to exit the muzzle. The barrel is</p><p>basically straight, and relatively calm.</p><p></p><p>(Read later about the "scatter node" which is the point</p><p>at which the bullets are being released from the bore</p><p>when the shock wave is at the muzzle. I call this area</p><p>the "scatter node" because it will produce a scattered group, </p><p>throwing flyers at random. This is the most</p><p>inopportune point of all for bullet release, the scatter node area</p><p>can be easily seen during an OCW test, and generally 1 to 2</p><p>powder graduations above the scatter node charge will have</p><p>you right in the OCW zone. The existence of the scatter node</p><p>is the main reason the conventional ladder (Audette) test often fails</p><p>to yield useful results--see OCW vs. Ladder on this site).</p><p></p><p>The OCW load would then have the optimal amount of</p><p>powder to push the bullet at just the right speed to be</p><p>exiting the muzzle when this shock wave is at the other</p><p>end (the chamber end) of the barrel.</p><p>This shock wave travels at the same speed regardless of</p><p>barrel length or girth (about 18,000 fps).</p><p>We note that OCW loads seem to perform very well</p><p>regardless of barrel length. (We're not considering non-</p><p>typical barrel lengths here). This makes sense because</p><p>the relationship between barrel time (the length of time it</p><p>takes the bullet to exit the muzzle) and the oscillating</p><p>shock wave is close to the same; in other words, in a short</p><p>barrel the shock wave reaches the muzzle and returns to</p><p>the chamber faster, but alas, the bullet reaches and exits</p><p>the muzzle faster also.</p><p>The harmonics which ride the main vibration node are</p><p>only of minor importance to accuracy in most cases. It</p><p>would appear that the effects of the subtle harmonic</p><p>vibrations can be largely negated with seating depth</p><p>adjustments, but a true OCW load will normally be</p><p>MOA or better in a good rifle without seating depth</p><p>tuning.</p></blockquote><p></p>
[QUOTE="flashhole, post: 1164701, member: 21375"] [url=http://optimalchargeweight.embarqspace.com/]OCW Overview - Dan Newberry's OCW Load Development System[/url] WHAT IS AN OPTIMAL CHARGE WEIGHT LOAD? With any given bullet and powder combination, there will be a specific amount of that powder which will cause the bullet to exit the muzzle at the "friendliest" portion of the vibration cycle. This does not necessarily correspond with the tightest velocity figures, however. Many load recipes have over the years become the "go to" recipes for trying out a new rifle. If your rifle fails to shoot one of these "tried and true" recipes well, you may well have a rifle integrity problem. Consider the Federal Gold Medal Match .308 win ammo. How can one recipe shoot so well in so many rifles? That's what we're after in the OCW load--a load recipe so stable and predictable that it does indeed rise above, and to some extent disprove the "all rifles are different" adage of lore... Think about it this way. Some kids like mashed potatos, some don't. Some kids will eat thier peas, some won't. Some kids like bananas, some hate 'em. But show me a kid that doesn't like*chocolate ice cream*and I'll show you one bizarre little character!*:) An OCW load is like chocolate ice cream to your rifle. If your rifle doesn't like the recipe, there is likely something weird about your rifle. If you perform the OCW load development properly, you are not (in the initial stages) seeking the optimal load for the test rifle. Heresy? Not really. There are many known "universal recipes" that work well in most rifles chambered for them. Ken Waters has made a pretty penny with his book "Pet Loads" on this concept. Many of the Waters loads have worked beautifully in my rifles, and acquaintances have had the same experience. Federal's Gold Medal Match .308 loads do well in practically any .308 not needing a gunsmith's attention. How can this be? If you subscribe to the philosophy that "all rifles are different," and therefore need individual loads tailored to accommodate their idiosyncrasies, how do you explain the near universal MOA performance of loads such as the Federal GMM? Universally good recipes do exist. Upon realizing this, my questions have been "How do such recipes work?" and "How can I develop such a load?" Recent conversations with very learned mechanical engineers are affording me some better understanding of just why an OCW load works so well in the majority of rifles chambered for the cartridge at hand. Here are some of the major points coming to light: Uniformity of velocity (meaning low extreme spreads of velocity) are definitely not*an indicator of the OCW zone. We are actually finding that in many cases the OCW zone does not have the tightest numbers--at least initially. Fine tuning of the recipe with seating depth variations and primer changes will improve the velocity consistency, but simply shooting a succession of graduated charges over the chronograph and looking for a tight velocity spread will not lead you to the OCW. As the reader comes to understand more about the main shock wave (link Chris Long's pages elsewhere in this webpage) it will become easier to understand how bullets with larger extreme spreads in velocity can still group tight (at closer ranges), while bullets with seemingly tiny extreme spreads may group poorly. You can tighten the extreme spread to improve long range accuracy AFTER you identify the OCW. Engineer Chris Long's model of barrel behavior suggests (simply put, and in part) that the initial shock wave, generated by the powder charge's ignition, travels at the speed of sound in steel (about 18.000 fps) from the chamber to the muzzle, then back, in a repeated pattern. When this wave is present at the muzzle, there is naturally much turbulence and obturation of the "roundness" of the bore at the muzzle. However, when this main shock wave has reverberated back to the chamber end, the muzzle is relatively stable. This window of opportunity, according to Chris, is the best time for the bullet to exit the muzzle. The barrel is basically straight, and relatively calm. (Read later about the "scatter node" which is the point at which the bullets are being released from the bore when the shock wave is at the muzzle. I call this area the "scatter node" because it will produce a scattered group, throwing flyers at random. This is the most inopportune point of all for bullet release, the scatter node area can be easily seen during an OCW test, and generally 1 to 2 powder graduations above the scatter node charge will have you right in the OCW zone. The existence of the scatter node is the main reason the conventional ladder (Audette) test often fails to yield useful results--see OCW vs. Ladder on this site). The OCW load would then have the optimal amount of powder to push the bullet at just the right speed to be exiting the muzzle when this shock wave is at the other end (the chamber end) of the barrel. This shock wave travels at the same speed regardless of barrel length or girth (about 18,000 fps). We note that OCW loads seem to perform very well regardless of barrel length. (We're not considering non- typical barrel lengths here). This makes sense because the relationship between barrel time (the length of time it takes the bullet to exit the muzzle) and the oscillating shock wave is close to the same; in other words, in a short barrel the shock wave reaches the muzzle and returns to the chamber faster, but alas, the bullet reaches and exits the muzzle faster also. The harmonics which ride the main vibration node are only of minor importance to accuracy in most cases. It would appear that the effects of the subtle harmonic vibrations can be largely negated with seating depth adjustments, but a true OCW load will normally be MOA or better in a good rifle without seating depth tuning. [/QUOTE]
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