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Where's the node ?
- Thread starter Az4z3L
- Start date
So, I’m in the garage doing some loading, and perusing my reloading notebook. Below are ten 5 shot groups with a 12” 6.5 Grendel AR and a PA PLX 1-8x LPVO. Now, I’m not a bench rest shooter, and this isn’t a benchrest gun, but the groups vary from ~1 moa to greater than 6 moa.
I loaded 50 at the “best” weight and went back to the range. I swapped the scope for a Leupold 5-25. Now, I only fired one group after zeroing with the “pet load.” I also fired a 5 shot group with a Hornady black factory load that is reliably sub moa in my “match” Grendel.
There are those that say “just pick a load that gives the speed you want.” Well, I’d prefer the 2500 fps of the 6 moa group, but have settled at a more modest 2300, as that charge weight gives better groups. I don’t need to put any more down the barrel to know which is which.
Oh, and Saterlee “nodes” don’t exist…
I loaded 50 at the “best” weight and went back to the range. I swapped the scope for a Leupold 5-25. Now, I only fired one group after zeroing with the “pet load.” I also fired a 5 shot group with a Hornady black factory load that is reliably sub moa in my “match” Grendel.
There are those that say “just pick a load that gives the speed you want.” Well, I’d prefer the 2500 fps of the 6 moa group, but have settled at a more modest 2300, as that charge weight gives better groups. I don’t need to put any more down the barrel to know which is which.
Oh, and Saterlee “nodes” don’t exist…
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I think you've got it for the most part.
So, yes. . . a tuner changes the barrel's frequency. Though the harmonics of a barrel is not simple as a simple single sine wave like in that pic, let's just KISS it.
In the end, it has to do with the alignment of the of barrel time and where in the harmonic that the bullet exits the muzzle. Change the frequency of the barrel for a fixed barrel time, you'll get a change in POI (as seen in that pic). Change the barrel time for a fixed frequency and again you'll get a shift in POI, since the muzzle will be pointing is a different direction when the bullet exits.If one is able to load their cartridges to where they get very small variances in velocity, dispersion on a target will be very small and whether you're in a "node" or not doesn't effect the dispersion for a group, but will show up just like in that pic. If one's cartridges produce a large velocity dispersion, then that's what we're going to see on target due to when the bullet leaves the muzzle in the harmonic. Finding the right powder charge, which effects barrel time, that's consistently at the point in the harmonic that moves the least will show up with less dispersion than a barrel times that vary and exit at different times in the harmonic. Consistent barrel time that minimizes the effects of being at a different spot in the harmonic is really what we're trying to find when trying to find a load that produces consistent small groups (like we do is OCW testing).
Tuners, which changes barrel frequency, only play a small role is reducing dispersion. Like, it won't make .5 MOA groups .2 MOA. . . especially if the cartridges produced can't have very consistent ignition and little velocity dispersion. The changes are so small, you've got to shoot really small to see it. Though POI is easy to see (e.g. my pic above). This is why, during OCW testing, I find comparing POI's relative positions along with shape and size of a small groups helps me determine which load tends to be the most consistent.
It's always a big challenge to keep everything consistent.
Once I find a load and tuner setting that work well together, I'll simply use the tuner to make adjustments to POI when I see it's being effected by atmospherics and/or barrel heat.
To your point on barrel vibration not being as simple as the chart there are multiple modes/frequencies. Unfortunately there is little out on the internet that discusses it for small arms. There are multiple military related articles for larger calibers and multiple barrel weapons. Here is a link to an article with some test and modeling data for a small arm weapon if anyone is interested.I think you've got it for the most part.
So, yes. . . a tuner changes the barrel's frequency. Though the harmonics of a barrel is not simple as a simple single sine wave like in that pic, let's just KISS it.
If one is able to load their cartridges to where they get very small variances in velocity, dispersion on a target will be very small and whether you're in a "node" or not doesn't effect the dispersion for a group, but will show up just like in that pic. If one's cartridges produce a large velocity dispersion, then that's what we're going to see on target due to when the bullet leaves the muzzle in the harmonic. Finding the right powder charge, which effects barrel time, that's consistently at the point in the harmonic that moves the least will show up with less dispersion than a barrel times that vary and exit at different times in the harmonic. Consistent barrel time that minimizes the effects of being at a different spot in the harmonic is really what we're trying to find when trying to find a load that produces consistent small groups (like we do is OCW testing).
Tuners, which changes barrel frequency, only play a small role is reducing dispersion. Like, it won't make .5 MOA groups .2 MOA. . . especially if the cartridges produced can't have very consistent ignition and little velocity dispersion. The changes are so small, you've got to shoot really small to see it. Though POI is easy to see (e.g. my pic above). This is why, during OCW testing, I find comparing POI's relative positions along with shape and size of a small groups helps me determine which load tends to be the most consistent.
It's always a big challenge to keep everything consistent.
Once I find a load and tuner setting that work well together, I'll simply use the tuner to make adjustments to POI when I see it's being effected by atmospherics and/or barrel heat.
Study on barrel vibration characteristics of typical sniper rifle - Extrica
The firing accuracy of sniper rifle is significantly affected by the barrel vibration induced by shooting load. The barrel vibration is an important parameter needing to be precisely controlled, whose measurement is less studied before. The vertical vibration characteristics of sniper rifle...
www.extrica.com
Varmint Al's work is actually very good (into the weeds good) but it doesn't have any actual correlating test data which I wanted to show. It can also be misleading when viewing models like Al's because the actual displacements typically get exaggerated (Don't show it in a management presentation!) There is also Chris Long's work that looks at the shock wave reflecting up and down the barrel that seems to have some merit and is included in QL I believe and is in Gordon's Reloading Tool.
There is a lot of papers available at the Defense Technical Information Center. Much of it is related to medium and large caliber long range weapons.
Defense Technical Information Center
Defense Technical Information Center Data Collection for COVID-19
discover.dtic.mil
I believe that the very existence of barrel harmonics and documented movement during firing demonstrates - that attempting to synchronize a bullet's exit with muzzle position is beneficial to accuracy. It is what I would define (as a complete layman) as load development.
It would also lead (at least me) to believe that there are wave patterns in accuracy where dispersion is going to be greater and lesser, depending on the inputs. I think that this is what many commonly refer to as the "node" (still hate that word).
This is of course simply stating something in a mere couple sentences that takes volumes to accurately detail.
It would also lead (at least me) to believe that there are wave patterns in accuracy where dispersion is going to be greater and lesser, depending on the inputs. I think that this is what many commonly refer to as the "node" (still hate that word).
This is of course simply stating something in a mere couple sentences that takes volumes to accurately detail.
Replying to the OP; you did not give us enough info on your targets, such as SD/ES and velocity. When I am testing for charge weight and seating depth, those two factors play a huge role in the decision in what to test at 1000 yards. Unless you are not going to shoot past 100 yards, you will have to test them at the distance you are going to shoot (whether it be hunting or some form of competition). One hole groups are great, but they don't necessarily translate at LR.
As someone posted earlier, test only one change at a time across all of the loads that you are thinking about using. Document everything you do, especially when you are old like me. A load that works at 65 degrees may go out of tune at 85 later on in the day even with the temp stable powders most of us today.
As someone posted earlier, test only one change at a time across all of the loads that you are thinking about using. Document everything you do, especially when you are old like me
. A load that works at 65 degrees may go out of tune at 85 later on in the day even with the temp stable powders most of us today.