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How far apart are accuracy nodes?
 Moderated by: Slingshot, Rockydog, klallen, DesertMarine, -6
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 Posted: Fri Jan 13th, 2017 10:47 PM
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papa45
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For those of you who have done serious ladder testing and identified multiple nodes for a particular load, how far apart are the nodes? 30, 50, 100 fps?

Is there a pattern to the pattern? For example: "smaller calibers are closer together, or "heavy loads are further apart, or "there is no rule of thumb that I can identify."



 Posted: Sat Jan 14th, 2017 12:11 AM
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swampshooter

 

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I've never found a pattern. Keeping good, complete notes is important.



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 Posted: Sat Jan 14th, 2017 12:33 AM
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Rockydog



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Here's a good illustration of how and why barrel pressures and bullet velocities impact accuracy nodes. Note that all deflections pictured are magnified to permit easier viewing of the concept.
http://varmintal.com/amode.htm



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 Posted: Sat Jan 14th, 2017 01:38 AM
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swampratt
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I found a node with Varget and 155gr bullet at about 2550 fps and another at 2815 fps 4.5 grain different in powder.

I could not get to the upper node with Lapua cases.
Long high BC bullet with short bearing surface always wanted to go fast.I never could find a slow node in the chart.

Begin at starting load and keep working up and still find nothing until you get to max or a bit past it in some books then they got tight. this was with both 308 and 30-06.

Be really hard to find a pattern in that quest.
I have found when you do hit a sweet spot with 30-06 or .308 you can be off a few tenths on powder charge and still not hurt the groups too much all the way to 300 yards.

I actually have a load for .308 that is not measured on a scale.. it is scooped and leveled off.
Nothing new there really.

But my little .223 you get off by 2 tenths either side and the group goes to double size



 Posted: Sat Jan 14th, 2017 02:03 AM
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STIHL
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Rockydog wrote:
Here's a good illustration of how and why barrel pressures and bullet velocities impact accuracy nodes. Note that all deflections pictured are magnified to permit easier viewing of the concept.
http://varmintal.com/amode.htm


Wow that is some serious information, I knew harmonics were pretty violent but seeing it amplified like that sheds a whole different light on the subject.

I've always understood it as you can't pinpoint accuracy nodes from gun to gun. There are too many variables, such as: barrel length and contour, barrel material and twist rate, weight of the gun, stock construction, bedded or floated, and that's just to list a few. Until you shoot it with a given load and projectile you can't know where it will fall. As swampratt pointed out some have very narrow nodes others have a wider node.



 Posted: Sat Jan 14th, 2017 04:10 AM
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runfiverun
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about every 300fps.
some of it depends on barrel length and diameter.
but right around 300 fps seems pretty close across the board.



 Posted: Sun Jan 15th, 2017 01:46 AM
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papa45
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Great feedback. Thanks. So, if the interval is about 250-300, it seems unlikely in most cases that one could find another practical node by just changing charge weight. For example, if a cartridge has a typical max velocity of 3000 fps and a node is found at 2900, the next higher node would produce excessive pressure, while the next lower node would give up a good deal of performance.



 Posted: Sun Jan 15th, 2017 11:13 AM
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swampshooter

 

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papa45 wrote:
Great feedback. Thanks. So, if the interval is about 250-300, it seems unlikely in most cases that one could find another practical node by just changing charge weight. For example, if a cartridge has a typical max velocity of 3000 fps and a node is found at 2900, the next higher node would produce excessive pressure, while the next lower node would give up a good deal of performance.

This is very true. But with heavier barrels I have found the accuracy nodes to be closer together.
IE; my 284 F-Class rifle. A Savage 22 lb. rifle with 1 1/2" straight taper 32" barrel, Nightforce 12-42x BR scope. The load I'm discussing is Lapua brass/180 gr. Sierra MK/H-4831sc/Fed. 210 primer. Accuracy nodes occur at 53 gr.& 54 gr. With 54 gr. having a slight accuracy edge. Average of 5, 5-shot groups at 300 yds.
52.5 gr./ 1.548 (discontinued after 3 groups)
53 gr./ 1.287" Velocity 2788 fps instrumental @ 10 yds.
53.5 gr./ 2.325" (discontinued after 2 groups)
54 gr./ 1.230" Velocity 2850 fps @ 10 yds.
54.5 gr./ 1.527" bolt lift a little stiff. Frequently had 4-shot knot of 0.800-0.810, by tuning with seating depth and/or neck tension this would probably have been best load, but bolt lift was starting to get stiff. Many top competitors shot this load.
55 gr./ 2.68" bolt lift stiff
I only shot 54 gr. when shooting at 1,000 yds.
53 gr. shot plenty good enough at 600 yds. and was easier on brass and rifle.



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 Posted: Mon Jan 16th, 2017 05:35 AM
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runfiverun
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you can find other nodes besides the main accuracy node.
your just getting 'the center of the whip' to use an expression from one 'best' to another 'best'.
you can find a pretty good one at the top or the bottom of the whip too.
you can then fine tune that whip node with primers or oal adjustments.
it might not be your 1/2" node but it is a good 3/4" node with a velocity closer to the one your looking for.
but your looking for the bullet to exit in the same place in the whip each time so more tuning/tweaking and exactness is needed to keep them all in that same spot.

for my hunting rifles I pick a bullet type and a velocity window I know the bullet will perform in then look for a node within that window.
it might be near an inch in accuracy, or do a bit better 20 fps above or below my desired window.
[close enough]
but I'm looking for results of another sort so I'm willing to make some sacrifices/compromises to try and get the best of both worlds.

a piece of paper at 1-2-3-600 yds don't know the difference of 25 fps in muzzle speed.
but paper at 1,000 will surely know when your bullet doesn't get there stabilized.



 Posted: Mon Jan 16th, 2017 03:31 PM
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ptaylortx
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I do OCW tests not ladders. but I find nodes are roughly 3% apart.



 Posted: Thu Jan 26th, 2017 12:37 PM
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huffmanite
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Fellow shooter at range did a ladder test with his very accurate 6BR rifle shooting at 100 yds. He takes great pains in his reloading for consistency

He shot 3 shot groups with .2 difference in his loads. Recall he had around eight sets of loads he fired. Sorry, do not recall the powder and etc., that he used, but shooting was done on a windless day with temps in the mid 70s.

Anyway, when finished shooting. you could easily see how the groups tightened and then opened up again as he shot the next higher .2 grain load. He had two sweet nodes on his target when done shooting at eight 1" bullseyes. Forget which, but I recall there was either .4 or .6 grain difference in his sweet nodes.

He will return to range next day using loads based on his two sweet nodes the day before. But this day he was working on the seating depth of his bullets. He had increased the amount of powder in his set of loads an amount each time he'd set the bullet closer to his lands. In other words, more he increased the case capacity for powder by moving the bullet closer to the lands, he increased his powder charge.

Will shoot this test of what happened to his groups by changes of bullet seating depth at four rows (eight bullseyes per row).

When he'd finished shooting, you could draw a diagonal line thru each sweet node showing on each row. In other words, imagine row one's sweet spot was bullseye one. Next row, with the bullet closer to lands and an increased powder charge, the sweet node was bullseye 2. On row three, with bullet closer to lands with same increase of powder, sweet node was bullseye three. Same results on row with bullseye four, now being the sweet node.



 Posted: Fri Jan 27th, 2017 03:23 AM
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SeabeeChief
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Found this on the web a few days ago while reading about nodes. It was calculated by an engineer.

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



 Posted: Fri Jan 27th, 2017 08:51 PM
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rocirish
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huffmanite wrote:
He will return to range next day using loads based on his two sweet nodes the day before. But this day he was working on the seating depth of his bullets. He had increased the amount of powder in his set of loads an amount each time he'd set the bullet closer to his lands. In other words, more he increased the case capacity for powder by moving the bullet closer to the lands, he increased his powder charge.


My question would be how did he determine how much to increase the powder as he was increasing case capacity.



 Posted: Thu Feb 9th, 2017 06:20 PM
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Offfhand
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If you hang around shooting ranges you'll hear some strange stuff. Same as browsing shooting forums. Makes you wonder who dreams it up.



 Posted: Fri Mar 3rd, 2017 01:42 PM
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huffmanite
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Recall my range friend doing his test, commenting something about how he came up with his powder charge increments, but don't remember his explanation.



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