The best tune to the node is the top and is the average or a little before the average. The bottom is also an alternative but may make problems with scope travel and a lower POI that long range shooters want to avoid. I was amazed when shooting a 6.5-284 loaded .1 of a grain more with each cartridge. Up the target 3 or 4 at the top then back down as loads went up. I think the little before the average at the top of curve is positive compensation????
Node difference
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SHOOTSMALLGROUPS.COM
It’s all on there, videos, discussion, love Erik’s approach. And the tuner brake. Many on here seem to dismiss it.
It’s all on there, videos, discussion, love Erik’s approach. And the tuner brake. Many on here seem to dismiss it.
Bill Norris
Back in the Day
The E C Tuner/brake works for me. I have one installed on three of my B R rifles and have been able to tune loads for different conditions with all three.
I've posted this pic before because of how apparent the sine wave pattern is. It's a tuner test but the same happens with powder charge and can also be seen with seating depth changes. The key, whether its with a tuner or by load changes is to systematically quantify group shape and size at small increments between all the way in tune to all the way out of tune. Frequency, in this application can be viewed as a measure of how far it is from the top or bottom of one nodal cycle to the next...ie, top to top or in the case of tuning a rifle, top to middle. Top being in tune and middle being the scatter node..or completely out of tune.
For all intents and purposes of this discussion, frequency is a constant. Even moving a tuner only has a small affect on frequency. Rather, it can change phase time pretty dramatically. What that means is basically by moving a tuner, we can shift the top of the sine wave left or right to coincide with bullet exit. Not trying to make this all about tuners but the principle is the same. Either way, we are optimizing the timing to where bullet exit happens when the bbl is at an anti-node, technically. An anti-node happens at top or bottom. A node is in the middle of a sine wave.
With my standard tuners, on a typical centerfire br contour barrel, there are only about 4-5 marks(only .004-.005" of tuner travel!) on the tuner between an anti-node and a node. This is important because knowing this allows you to break down relative tune to only 4-5 increments and can be interpreted by group shape and size. That's how you know what to do with the tuner and when, in terms of how far to move it. It also explains why so many people feel like the ocw method seems to work or at least get ya very close. Because you're never really far from in tune if you break it down to the distance between the node and anti-node of a single nodal cycle. I mentioned earlier that I had been able to do the same thing with a ppc and n133 powder. What I found is that 1 mark on my tuner is very near the equivalent to .3 gr of powder. There are too many variable for me to say the same about other powders and in different cartridges and that also part of why I can't agree with the previous statement regarding 3% powder increments across the board. But I say this to show that both methods work on the same principle and that yes, it can be quantified, the value of a mark on a tuner vs powder charge increments. Either methos is about timing bullet exit with optimal muzzle position.
Oops! Almost forgot to post the picture. I didn't shoot this test. It was fired by a customer but clearly shows the sine wave.
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Thx, I use a slightly different approach these days for long range tuning that I won’t get into just now just had that question lingering.
Jarhead6870
Gold $$ Contributor
It is my opinion that a change in seating depth or neck tension changes pressure minutely whereas more/less powder changes it much more. Tuners don't alter pressure and are another game altogether.
Since the discussion started off asking about OCWs and the 3% node separation, I though I'd show an OCW test I did for a 300 PRC shooting Hornady 225 ELD-Ms over H1000. Again, this was shot off a bipod using a rear squeeze bag following Dan Newberry's instructions of shooting the test in "round robin" fashion, meaning I shot one shot of each charge weigh before shooting a second and lastly the third. I got up after each shot and waited about 1 minute between shots. This also means I had to build a shooting position for each of the 24 shots. Now some may ask "why not use a front rest to establish a more solid rest for the rifle?". Well I am of the belief, again I'm not a Benchrest or F-Class shooter, that when shooting prone off a bipod with a rear bag that management of the recoil impulse is important in the way a rifle shoots. Simply put; if this is how I shoot, then this is how I should test.
To the test:
Per Dan's instructions for analyzing the target, after connecting the dots for each group and finding their centers, we are looking for 3 consecutive charge weights where the "center" of the group is in the same RELATIVE location to the POA (Point of Aim). Size of the group is not important as you can tune the charge weight with a seating depth test to tighten things up and remember, we are shooting this one shot at a time getting out of the rifle between shots. Charge weights 74.2, 74.8 and 75.4 are 3 in a row whereas 76.0 shifted. Charge weights 76.6, 77.2 and 77.8 also give us 3 in a row with 78.4 shifting. From this target, I concluded that I had 2 nodes and taking the center charge weight from each I could use charge weights 74.8 or 77.2 grains and expect success. The shifting at charge weights 76.0 and 78.4 indicate to me that these are the scatter nodes. Just in case anyone was wondering, I did the math and both nodes, accuracy and scatter, are 3% apart and the scatter nodes are 1.5% above and below the accuracy nodes.
Since this rifle is primarily used at 1800 yards and out, I chose 77.2 to get the velocity. I shot a "tall" target test while using a chronograph for 10 shots; muzzle velocity was 2923 fps with an ES of 15 and SD of 4.6.
An opportunity arose to go shooting before I had a chance to verify my elevations so this rifle went from 100 yard testing to a target at 1900 yards; I had this load on target in 3 shots with only 0.2 MIL of elevation adjustment. Once this correction was made, I let less experienced shooters who hadn't shot over 880 yards shoot so they could experience the pleasure of hitting something at over a mile. Out of the 17 rounds they fired that day, they had 5 more hits on target.
I posted this not to brag but to show that I have had success with the OCW method. Some may say it was luck but I've had this type of success using the OCW with all of my rifles. This includes shooting my 6.5x47 using Berger 140s at a mile...but it took me 5 shots to get on target (damn wind).
Since the discussion started off asking about OCWs and the 3% node separation, I though I'd show an OCW test I did for a 300 PRC shooting Hornady 225 ELD-Ms over H1000. Again, this was shot off a bipod using a rear squeeze bag following Dan Newberry's instructions of shooting the test in "round robin" fashion, meaning I shot one shot of each charge weigh before shooting a second and lastly the third. I got up after each shot and waited about 1 minute between shots. This also means I had to build a shooting position for each of the 24 shots. Now some may ask "why not use a front rest to establish a more solid rest for the rifle?". Well I am of the belief, again I'm not a Benchrest or F-Class shooter, that when shooting prone off a bipod with a rear bag that management of the recoil impulse is important in the way a rifle shoots. Simply put; if this is how I shoot, then this is how I should test.
To the test:
Per Dan's instructions for analyzing the target, after connecting the dots for each group and finding their centers, we are looking for 3 consecutive charge weights where the "center" of the group is in the same RELATIVE location to the POA (Point of Aim). Size of the group is not important as you can tune the charge weight with a seating depth test to tighten things up and remember, we are shooting this one shot at a time getting out of the rifle between shots. Charge weights 74.2, 74.8 and 75.4 are 3 in a row whereas 76.0 shifted. Charge weights 76.6, 77.2 and 77.8 also give us 3 in a row with 78.4 shifting. From this target, I concluded that I had 2 nodes and taking the center charge weight from each I could use charge weights 74.8 or 77.2 grains and expect success. The shifting at charge weights 76.0 and 78.4 indicate to me that these are the scatter nodes. Just in case anyone was wondering, I did the math and both nodes, accuracy and scatter, are 3% apart and the scatter nodes are 1.5% above and below the accuracy nodes.
Since this rifle is primarily used at 1800 yards and out, I chose 77.2 to get the velocity. I shot a "tall" target test while using a chronograph for 10 shots; muzzle velocity was 2923 fps with an ES of 15 and SD of 4.6.
An opportunity arose to go shooting before I had a chance to verify my elevations so this rifle went from 100 yard testing to a target at 1900 yards; I had this load on target in 3 shots with only 0.2 MIL of elevation adjustment. Once this correction was made, I let less experienced shooters who hadn't shot over 880 yards shoot so they could experience the pleasure of hitting something at over a mile. Out of the 17 rounds they fired that day, they had 5 more hits on target.
I posted this not to brag but to show that I have had success with the OCW method. Some may say it was luck but I've had this type of success using the OCW with all of my rifles. This includes shooting my 6.5x47 using Berger 140s at a mile...but it took me 5 shots to get on target (damn wind).
@gunsandgunsmithing
Thx Mike for the detailed explanation, I have absolutely zero experience with tuners but always wondered how they worked. After a pressure ladder we use a modified version of an ocw but in a one point of aim steady pace round robin format focusing on stability and overlap as we go in and out of tune and what I see is very small groups just before the load goes out and take you to either the promised land or Pluto so I stick with small and stable which is more towards the middle of the node.
Just a follow up thought that I don’t know if it really matters being the top or the bottom of the wave because out of tune rifles shoot all directions.
Jim
Thx Mike for the detailed explanation, I have absolutely zero experience with tuners but always wondered how they worked. After a pressure ladder we use a modified version of an ocw but in a one point of aim steady pace round robin format focusing on stability and overlap as we go in and out of tune and what I see is very small groups just before the load goes out and take you to either the promised land or Pluto so I stick with small and stable which is more towards the middle of the node.
Just a follow up thought that I don’t know if it really matters being the top or the bottom of the wave because out of tune rifles shoot all directions.
Jim
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CharlieNC
Gold $$ Contributor
Assume your shots have variable velocity. At a short distance this translates into a minimal moa impact difference on a target, vs at long range, due to gravity. In addition the barrel vibrates vertically (sine wave). Compensation considers the bullet exit is timed to the part of the sine wave such that the vertical impact due to gravity is offset by barrel vibration. So at a short distance the optimum exit is at or near the top/bottom of the vibration since there is less gravitational effect to offset. On the other hand at long range the gravity effect due to variable velocity is significant, and ideally the bullet timing is on the steep part of the sine wave where higher velocity yields a negative (drop) slope which perfectly offsets gravity. From the harmonics perspective this defines a node. Charge weight is a major means to tune in the bullet exit timing to minimize effects of velocity. And if you run a "wide" enough charge weight evaluation (eg ladder) and adjust the vertical impact by subtracting the effect of gravity (eg using a ballistic calculator) then the target will exhibit the sine wave due to barrel vibration; in his book Vaughn presents several graphs demonstrating this.
@CharlieNC
Thx for that explanation, I struggle typing my thoughts these days so I appreciate your posts.
Thx for that explanation, I struggle typing my thoughts these days so I appreciate your posts.
@gunsandgunsmithing
Pretty cool that all that movement is by turning a tuner.
Ok so here’s a follow up question and perhaps you’ve already answered this but do you contribute the movement ( not the shape) to slight pressure changes as in combustion or harmonics ?
Pretty cool that all that movement is by turning a tuner.
Ok so here’s a follow up question and perhaps you’ve already answered this but do you contribute the movement ( not the shape) to slight pressure changes as in combustion or harmonics ?
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Old Navy
Gold $$ Contributor
Excellent shooting.
I can't take the credit for that. As said, a customer shot this test target but a good short range br rifle, in good conditions, should shoot similarly to this test. It needs to be done only with flags and in really good conditions. Ultimately, the test is only a single 3 shot group at each tuner setting along the way. What makes it useable is that you should get predictable and repeatable results for a couple of groups on both sides of a sweet spot. As long as we get that, you're looking at about five groups rather than one, to determine if it's really a good and repeatable setting. Without flags, there's simply no good way to know why a shot comes out(or in) of a group. I like to see the groups open a little more than these did when it's out of tune. Barrel stiffness is a big factor in that. Bigger groups when out of tune are simply easier to read how well the gun is tuned..or not. Actually, this has prompted me to go to slightly smaller and/or longer contours than I use to use on most of my builds. To a point, I prefer a little less stiffness. I call it "talking to me." They'll show tune more apparently than a really stiff bbl. And fwiw, a fatter bbl is not necessarily stiffer overall. Length has more to do with stiffness than bbl od. In my short range stuff, I've settled on my own contour than is about .900 at 24" long. It's pretty close to a std LV contour, though.
Alex Wheeler
Site $$ Sponsor
I adjust powder charge 1/2% at most. When fine tuning, 1/3% or less. 3% is close to node spacing. So if you are off a node and move 3% you will still be off a node about the same as before.
Alex Wheeler
Site $$ Sponsor
Virtually everything you can do changes in bore time..so yes. It doesn't even have to change muzzle velocity at all to change the pressure curve and timing.
My way of thinking, giving the velocities are the same, a bullet
farther into the lands leaves the barrel first. It's where that bullet
is leaving in relation to what the barrel is doing in it's harmonic
swing, is key to this problem. So my last test involved finding a
node around 2930, I went .003 into the lands and the groups
closed up. I then added powder next, and the groups opened
back up. For me, I had to manipulate around that 2930 with
seating. Only the next match will tell.....
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