Barrel node and its correlation to ES/SD?

[done111]

I have run various powder amount variations and evaluated the groups to find a good node at 100 yards. I have a magnetospeed and I have chronographed this load at a later time and I am disappointed in the extreme spread and standard deviation, 33 and 12 fps respectively.

Is there a direct relation of better ES/SD with the barrel node. If so, how? I am thinking that "speed nodes" and barrel whip nodes may be fairly independent and you only hope they might be close to each other. Now that I am sending these 6.5 140 ELDM bullets out to 1000, its obvious in my vertical variation that the velocity needs to be tuned up.

I don't have a higher dollar doppler chronograph, only a magnetospeed. I'm thinking I can shoot for nodes with the bayonet on there, knowing POI is shifting and hopefully the bayonet doesn't change its affect from shot to shot or from group to group. I can work mainly with the velocity measurement and hope I get a decent group/ node at 100 yards too?

How are shooters with a magnetospeed finding the perfect load out to 1000 yards?

Don

 

[smoooth]

 

[TimB]

Dan Newberry, who invented the OCW system, claims that ES & SD are NOT indicators of a OCW node. It's OK to use your Magneto speed while running the OCW test but it will affect POI (for me about 1.5 inch higher). For long range you will need a higher velocity OCW node, so keep increasing your charge weight (without pressure signs) until you find it. If you experience pressure before you see a node, you may have to change powder. Once you find a OCW node at the higher velocity, you can then tweak seating depth and bullet tension to improve ES/SD.

 

[Texas10]

It's been my experience that if the magneto speed bayonet shifts position on the barrel during recoil, it'll act to tune or de-tune barrel harmonics and change group position and size. So, like you I develop the load for accuracy/consistency and then measure velocity, SD, ES. If it shoots great, but measures horrible, its time to try a different powder or primer.

There's no doubt that the LabRadar is the better piece of equipment for load development however, I'm not one to afford that kind of luxury, and am not even sure it's necessary for 100 yd load development. IMOP, long range load development is an entirely different science requiring careful evaluation of a thousand different variables, all of which have a cost associated with them.

 

[rijndael]

and hopefully the bayonet doesn't change its affect from shot to shot or from group to group.

Just be careful with the bayonet sliding closer to the muzzle. You need to make sure it's solid. IME, if it slides with each shot, it will do more than impact the POI. I have a black sharpie reference line on my stainless barrel. It's a quick visual indicator to make sure it's not sliding, and I like placing it on the same spot on the barrel each time.

 

[chop house]

I'm not one to afford that kind of luxury, and am not even sure it's necessary for 100 yd load development. IMOP, long range load development is an entirely different science

i pretty much agree here. although, if someone was willing to sell me one for $100....

 

[Bart B.]

I have run various powder amount variations and evaluated the groups to find a good node at 100 yards. I have a magnetospeed and I have chronographed this load at a later time and I am disappointed in the extreme spread and standard deviation, 33 and 12 fps respectively.

Rifles with ammo producing those numbers have been shooting sub MOA groups at 1000 yards for decades.

What, exactly, is a "good node?"

 

[Richard Coody]

well i don't do load development with a cronograph. they are just another distraction. i let the target tell me what the rifle likes. reloading manuals can give you a pretty good idea of what velocity you can expect from certain loads. i also am not looking for accurate loads at max.

once you have found your charge weight and seating.depth then you can break out the crony to establish a drop chart. a little tweaking of charge or seating depth at this point may reduce es and sd but i find with truely accurate powder charges and good control over neck tension your SDs will be fine.

 

[normmatzen]

there is a fellow in Australia who published a small book (We call it the "Blue Book") that outlines how to tune a rifle. He first shoots round robin style 5 shot groups with each group different powder loads, say, nominal with 1% increases and decreases. When done, graph it with EXCEL and do a 4-5th order poly curve fit to find the load for best ES. That is where we stop as we also use barrel tuners so we take the load we found above and tune for best performance.
The writer of the book also explains how to shorten the barrel for final tune.

This ES tune we do with a MagnetoSpeed on the barrel as this tune sets the "traveling donut" resonance, similar to an organ pipe. This is not effected by the tuner or the magnetospeed, at least importantly. Then, we take off the MagnetoSpeed and tune the tuner for best groups at particular distances.

 

[Capt. Oblivious]

Same way I do it, been doing it for a long time actually just never posted it on youtube

 

[Bart B.]

This ES tune we do with a MagnetoSpeed on the barrel as this tune sets the "traveling donut" resonance, similar to an organ pipe.

What is "traveling donut" resonance?

If it's the shock wave from the round firing, it's round trip frequency in the barrel is fixed and cannot be changed.

 

[normmatzen]

Bart,
Yes and yes!
The longitudinal resonance IS fixed and there is an Excel somewhere on the net to calculate what the time per node based on exact barrel length.

So, that is why we do 5 sets of 5 shot groups with increments of ~1% in powder weight. I then measure each shot with my MagnetoSpeed and take this data home (from the 25 shots as well as sighters) and calculate the average velocity and SD of each group. I don't use the SD tho instead take the ES from each 5 shot group. I plot the ES vs charge weight in Excel, then do a curve fit of the data to a 4th or 5th order Polynomial. This fills in the missing data in the test data to a pretty good level. I do this at 200 yd and shoot at 50 yd small bore 5 bull targets and take the targets home for grins.

I then load bullets with the lowest ES point on the curve and go back to the range and tune my tuner for best group.

In short, I don't try to change the longitudinal resonance, just match the barrel time to that resonance! The resonance is a function of barrel length and speed of sound in stainless steel! When the load is tuned correctly, if a future shot is slightly hotter, it will not reach the end of the barrel at the correct time and slow down a bit. If it is a bit low, it will also not hit the node but will be speeded up! So, the load is tuned for best ES. The tuner then is used to tune the beam oscillation or whip.

 

[done111]

In short, I don't try to change the longitudinal resonance, just match the barrel time to that resonance! The resonance is a function of barrel length and speed of sound in stainless steel! When the load is tuned correctly, if a future shot is slightly hotter, it will not reach the end of the barrel at the correct time and slow down a bit. If it is a bit low, it will also not hit the node but will be speeded up! So, the load is tuned for best ES. The tuner then is used to tune the beam oscillation or whip.

I might need a little more help understanding this. What is being matched to resonance? The time that the bullet exits the barrel? Resonance is generally expressed in units of frequency, such as cycles per second (Hz). Is there some frequency being generated that can be altered that is matched to a natural frequency of the barrel and thus resonance is occurring/created?

Also, the statement where it is mentioned that when properly tuned a hot load will slow down some and a low speed load will speed up. I don't understand how this occurs as well. I can see that that would lower your extreme spread, but I don't see the physics behind that statement.

Thanks for any additional explanation that can be given to help me understand what is being done here.

Don

 

[gilmillan1]

You guys are too technical. You are over thinking this whole deal. Es are acquired by powder charges. Get a powder charge that has the best es. Then play with seating depth for accuracy. 3 thou at a time. Then adjust the tuner if you have one. That's it. Nothing magical or technical.

 

[brantfredrickson]

I have run various powder amount variations and evaluated the groups to find a good node at 100 yards. I have a magnetospeed and I have chronographed this load at a later time and I am disappointed in the extreme spread and standard deviation, 33 and 12 fps respectively.

Is there a direct relation of better ES/SD with the barrel node. If so, how? I am thinking that "speed nodes" and barrel whip nodes may be fairly independent and you only hope they might be close to each other. Now that I am sending these 6.5 140 ELDM bullets out to 1000, its obvious in my vertical variation that the velocity needs to be tuned up.


Don

Whether you are using OCW, Audette Ladder, or 10 round load development to find a node, you are looking for a minimum change in velocity per change in charge weight. That's different from a low ES/SD which is minimum change in velocity for a single charge weight. I keep an eye on the ES/SD's but I look for the minimum change in velocity per charge weight. In OCW that would be two smaller groups with adjacent charge weights. Or in an Audette ladder two bullets holes that are close to each other with adjacent charge weights. And in 10 round load development two velocities that are close to each other with adjacent charge weights.

 

[CharlieNC]

I would like to see a post showing a ladder/ocw trial reporting both target and chrono performance shot simultaneously to demonstrate the chrono alone will gurantee what the target reports. My load developments have not shown the chrono alone is adequate. It is straightforward to understand harmonic barrel movement shows up on the target, but I have no concept nor have read any definitive report regarding why velocity would likewise respond. Being open minded, I can be easily convinced with a valid target vs chrono comparison.