Node !!

[big5ifty]

...the generally accepted definition of node (using a ladder or OCW method) that seems to be the following:
"A node is where varying powder charges have little or no effect on the muzzle velocity and vertical shot dispersion on the target."

That is not a node definition using OCW, as far as I understand it.

An OCW node is the point around which successive 1% increments in charge weight tend to group, with no reference to velocity.

OCW is repeatable.

By definition, if it's not immediately repeatable, it's not a test.

 

[Straightshooter1]

Why? I do too to a degree because I think there are both, but due to gravity, bbl movement and groups appear vertically biased(not only). I've posted several pics of targets on here. I can see where that applies to a degree based on the fact that groups don't form only in the vertical or in the horizontal, though. So I'm just wondering your logic is all. Not saying it's right or wrong, though. I think my tuner test shows a clear pic of what happens on the target but it can't possibly show every single force even if they are repeatable. Repeatable group shapes are undeniable if you see enough test targets. It's along the lines of 95+% of the time that the groups have the same shape patterns at different tuner mark intervals. That's freakin huge and I don't much care what anyone says. I see more test targets than possibly anyone because of how I do tuner sales. I only do them by phone, give very specific test instructions and I predict group shapes respective to tuner settings before the customer even shoots the test. That's only possible one way.

I feel you might be right about the vertical bias and I wonder if that is largely do to the impulse (a different response in the barrel from the harmonics) that travels down and back in the barrel . . . ???

When I visualize a sort of corkscrew sine wave harmonic of the barrel, there's still sine wave nodes and anti-nodes and they changes position radially due to the variations involved with the other elements in the internal ballistics. This is what I tend to attribute to the shape of groups. Also, I'm not saying I right . . . just that's how, at this point, my thinking puts it all together. You might say, it's like my Theory of Everything.

 

[praveen]

That is not a node definition using OCW, as far as I understand it.

An OCW node is the point around which successive 1% increments in charge weight tend to group, with no reference to velocity.

OCW is repeatable.

By definition, if it's not immediately repeatable, it's not a test.

Actually, you are saying the same thing.

"An OCW node is the point around which successive 1% increments in charge weight tend to group, with no reference to velocity."

Let's say the node point is 40 grains of powder.
Try some successive 1% increments...

40.4, 40.8, 41.2, 41.6, 42

We can at least agree that ( more powder => more velocity ).

In that case, the velocity produced by 40.4 is going to be greater than 40 grains and 40.8 grains will produce more velocity than 40.4 grain... and so on.

This will hold true for all starting powder charges. And I just ran a load development charge with 0.3 grain increments. And sure enough, the velocities kept increasing with every charge increment.

Now, once a muzzle velocity has been established, the barrel would make no influence on the bullet from that point. Internal ballistics is done at that point.
Only external ballistics come into play. The projectile equation with all the various external influences added to it. And the very basic projectile equation is directly proportional to the initial velocity.

So, then there is no way that any barrel/internal ballistic phenomenon would make a higher velocity bullet group with a lower velocity bullet.

Now, if you would say that increasing charges somehow DO NOT end up increasing the velocity, that is something to be mulled over.

 

[William Vogel]

Here’s something I would like to share. I began load deployment by simply using other people’s options on powder type for cartridge. I also relied on the powder burn rate chart. I shot a lot of cartridges and found some good loads. I then downloaded Gordon’s Reloading Tool. Something I found is that it predicted that many of my loads would have bullet exits before burn out. I bought powders that were predicted to burn out BEFORE bullet exit. By this time I’ve collected lots of data on my rifles through shooting previous loads. By using powder that Supposedly burns out, my ES and SD are much better. My groups have gotten tighter. I’ve found that with GRT, the burn rate chart is almost useless except for steering me towards a powder.

 

[chop house]

I do too to a degree because I think there are both, but due to gravity, bbl movement and groups appear vertically biased(not only). I've posted several pics of targets on here. I can see where that applies to a degree based on the fact that groups don't form only in the vertical or in the horizontal, though.

how does group shape change with different lug configurations? if a typical two lug is mounted 90* rotated in a stock do they become biased horizontal? are three lug groups 'naturally' more round? inquiring minds...

 

[CharlieNC]

Actually, you are saying the same thing.

"An OCW node is the point around which successive 1% increments in charge weight tend to group, with no reference to velocity."

Let's say the node point is 40 grains of powder.
Try some successive 1% increments...

40.4, 40.8, 41.2, 41.6, 42

We can at least agree that ( more powder => more velocity ).

In that case, the velocity produced by 40.4 is going to be greater than 40 grains and 40.8 grains will produce more velocity than 40.4 grain... and so on.

This will hold true for all starting powder charges. And I just ran a load development charge with 0.3 grain increments. And sure enough, the velocities kept increasing with every charge increment.

Now, once a muzzle velocity has been established, the barrel would make no influence on the bullet from that point. Internal ballistics is done at that point.
Only external ballistics come into play. The projectile equation with all the various external influences added to it. And the very basic projectile equation is directly proportional to the initial velocity.

So, then there is no way that any barrel/internal ballistic phenomenon would make a higher velocity bullet group with a lower velocity bullet.

Now, if you would say that increasing charges somehow DO NOT end up increasing the velocity, that is something to be mulled over.

Search positive compensation for extensive discussion. The muzzle is moving so different velocities launch at different angles.

 

[ebb]

Read the book Rifle Accuracy Facts by Harold Vaughn

 

[praveen]

Search positive compensation for extensive discussion. The muzzle is moving so different velocities launch at different angles.

I’m reading it now.

 

[dcali]

As far as I can tell, the use of "node" as jargon came about right around the time that the concepts of barrel vibration and positive compensation were becoming widely known. At the time, maybe 20-25 years ago, a common misunderstanding was that barrels vibrated in a sine wave, and you could adjust your charge weight to coincide with one of the nodes on the sine wave. That explanation is mostly incorrect.

Today, people seem to get that for the most part, but the terminology has stuck. Today, "node" is generally used to mean "good load", or sometimes pertaining to one specific variable. Like "velocity node", "seating depth node". It's an unfortunate misnomer that causes a lot of confusion.

Adding powder increases velocity on average - always. This is easily provable. I've done it, as have many others. Shoot 30 rounds with varying charges and make a graph. You will see a straight line with all the points within the expected statistical variation.

I think the "every barrel is different" thing is overblown. Today's custom barrels are pretty good, and while you'll see very minor differences, they're basically the same. If you get two barrels from the same vendor and chamber them identically, you'll have very close to the same results. Maybe not by gnat's ass benchrest competition standards, but by most shooters' standards.

The reason for varying velocity hitting at the same vertical is that the barrel whips a very small amount when fired. Depending on when the bullet leaves, it will be sent off on a slightly different trajectory. Sometimes, that slight variation in muzzle movement can compensate for a slight variation in velocity, and you wind up hitting the same point. This is what is known as "positive compensation" these days. It was first observed over 100 years ago, but only managed to filter into common understanding in the last 20 years or so.

 

[dcali]

So, in general the barrel vibrates not with its natural frequency but with a forced frequency that is forced by an external force. In this case, the contained explosion. Of course its more complex then this because the pressure is changing and there’ll be multiple waves at any given point of time. So, using this wave explanation, we can see that there are going to be times in a barrel’s vibration when it moving the least. But this will be true for every single powder charge and not a particular load. Doesn’t exactly explain why certain charges become a node.

You've almost got it. Part of it at least. Barrels (like any object) have multiple resonant frequencies. how they vibrate depends on the frequency (frequencies, really) of the driving force. In very simple systems it's possible to excite only one "mode" or resonant frequency. In real world systems, many get excited at the same time. So you wind up with a complex dynamic motion of the muzzle. It's moving and deforming in 6 degrees of freedom - sideways, back to front, up and down, plus the three axes of rotation (roll, pitch, yaw). The precise orientation and motion of the muzzle as the bullet leaves determines the initial conditions for the bullets path.

Different charges will produce different velocities and drive the barrel vibration slightly differently (because it changes the driving force). When put all together, you can have the vibration cancel out the velocity variation. One of the predominant driving forces in a rifle is the imbalance in support and mass distribution in the vertical plane. Because of that, you get a large up/down component to the muzzle motion. That's why positive compensation is so easy to see relative to other barrel motion effects. It's not possible to calculate this motion precisely enough to be useful. Measuring it is extremely difficult and impractical. But we can see the effects on the target.

It's important to note that this is not all there is to what makes a load good. It's my belief/opinion that there is simply a great deal we do not understand. Some things we do, but we probably don't know more than we do. Some things we kind of understand but not well enough to be truly useful.

At the end of the day, we're rapidly approaching academics at this point. That's fine and I personally enjoy it for its own sake, but you don't need to understand how something works if you just want to print small groups. Knowing that it works is enough.

 

[K22]

There are a lot more loading experts than good shooters.

In my non-expert opinion, this is one of the truest statements I have personally witnessed in my 50+ years in the shooting sports including 30 years of competitive pistol shooting. My only addendum is that I would expand that concept to include hunting and firearms cleaning.

 

[Bugs]

If my wife node how much I've spent shooting benchrest, I would be living out in the shed.

 

[K22]

In recent years I have made a hobby of trying to help shooters get better results. One fellow that I finally have given up on has always had a great deal of trouble accepting anything that does not fit within "it seems to me". The trouble is that what is logical to him does not work very well, and his rifle does not care about his "logic". My advice to everyone is to do well thought out experiments and to believe your targets. For most of us, the goal is to shoot better. With regard to your question. There will generally be more than one powder charge that works, but some nodes are wider than others. This is determined by experimentation. Other factors can influence node width. In the last few years tuners have come into more common use in competition, and some of those who use them tell us that they tend to broaden nodes, in that case, meaning that a given load will work through a broader temperature range. Often, we can only know that a thing works, but lack the proper equipment and or budget to prove why.

There is real satisfaction in helping a fellow shooter, at least to me. My contribution has come more from the performance side rather than the technical side. This goes back to my days in the Army when I was a part time firearms instructor preparing doctors being sent to Vietnam, many of which had never fired a weapon of any kind.

I spent a lot of time at the range these days, more so since my declining physical condition is limiting my varmint and predator hunting days which are coming to an end.

I encounter many guys at the range that are preparing for an expensive big game hunt. While most have expensive rifles and scopes, many need help in sighting in their rifle. I've seen just about everything, improper scope eye relief, scope mounted off center, scope mount too high, rifle resting on sling, barrel resting on wooden blocks, use of lead sleds which yield POI different than natural holding positions in the field, less than optimum elevation sight in for POI for the type of hunt, etc., etc.

Of course, I only offer assistance if they ask, most do, and it is a great reward for me personally to help a fellow shooter get his rifle hunting ready for perhaps a hunt of a lifetime.

I totally agree with you about the experimentation concept in other facets of the sport. I have solved many of my own shooting problems with such an approach. "Believe your target" is my core philosophy.

 

[JEFFPPC]

If my wife node how much I've spent shooting benchrest, I would be living out in the shed.

Mike, my wife I are both sitting here lauging.

 

[Doom]

You've almost got it. Part of it at least. Barrels (like any object) have multiple resonant frequencies. how they vibrate depends on the frequency (frequencies, really) of the driving force. In very simple systems it's possible to excite only one "mode" or resonant frequency. In real world systems, many get excited at the same time. So you wind up with a complex dynamic motion of the muzzle. It's moving and deforming in 6 degrees of freedom - sideways, back to front, up and down, plus the three axes of rotation (roll, pitch, yaw). The precise orientation and motion of the muzzle as the bullet leaves determines the initial conditions for the bullets path.

Different charges will produce different velocities and drive the barrel vibration slightly differently (because it changes the driving force). When put all together, you can have the vibration cancel out the velocity variation. One of the predominant driving forces in a rifle is the imbalance in support and mass distribution in the vertical plane. Because of that, you get a large up/down component to the muzzle motion. That's why positive compensation is so easy to see relative to other barrel motion effects. It's not possible to calculate this motion precisely enough to be useful. Measuring it is extremely difficult and impractical. But we can see the effects on the target.

It's important to note that this is not all there is to what makes a load good. It's my belief/opinion that there is simply a great deal we do not understand. Some things we do, but we probably don't know more than we do. Some things we kind of understand but not well enough to be truly useful.

At the end of the day, we're rapidly approaching academics at this point. That's fine and I personally enjoy it for its own sake, but you don't need to understand how something works if you just want to print small groups. Knowing that it works is enough.

Great couple of post.

 

[RickyK]

If my wife node how much I've spent shooting benchrest, I would be living out in the shed.

Best answer in this thread !

 

[JFrank]

As far as I can tell, the use of "node" as jargon came about right around the time that the concepts of barrel vibration and positive compensation were becoming widely known. At the time, maybe 20-25 years ago, a common misunderstanding was that barrels vibrated in a sine wave, and you could adjust your charge weight to coincide with one of the nodes on the sine wave. That explanation is mostly incorrect.

Today, people seem to get that for the most part, but the terminology has stuck. Today, "node" is generally used to mean "good load", or sometimes pertaining to one specific variable. Like "velocity node", "seating depth node". It's an unfortunate misnomer that causes a lot of confusion.

Adding powder increases velocity on average - always. This is easily provable. I've done it, as have many others. Shoot 30 rounds with varying charges and make a graph. You will see a straight line with all the points within the expected statistical variation.

I think the "every barrel is different" thing is overblown. Today's custom barrels are pretty good, and while you'll see very minor differences, they're basically the same. If you get two barrels from the same vendor and chamber them identically, you'll have very close to the same results. Maybe not by gnat's ass benchrest competition standards, but by most shooters' standards.

The reason for varying velocity hitting at the same vertical is that the barrel whips a very small amount when fired. Depending on when the bullet leaves, it will be sent off on a slightly different trajectory. Sometimes, that slight variation in muzzle movement can compensate for a slight variation in velocity, and you wind up hitting the same point. This is what is known as "positive compensation" these days. It was first observed over 100 years ago, but only managed to filter into common understanding in the last 20 years or so.

If I lived to be 100 and practiced every day, I still could not describe it any better than you have.

 

[jackieschmidt]

I have had a pretty successful shooting career and I never looked for a node. I did not know what OCW was, never heard of a ladder. What I did learn by shooting lots of matches and talking to successful competitors and going thru lots of barrels was three things. "1, If you do all your barrels with your reamer with one smith your loads barrel to barrel will be extremely close. #2 Most important.....you need to develope a loading process that works for you. #3 Unless you can get back to back 3 or 4 shot groups in the zeros and low ones, keep working at it. Ok First free one....I have been using tuners for about 15 years, others use to laugh at me, I never found my load with one. I use them to keep my load in tune. Second free one......if you don't love your flags your in for a long ride. There are a lot more loading experts than good shooters.

Great statements,

I fall into this category. I feel like my Rifles, bullets, my loading techniques, everything I do prior to touching the trigger takes a back seat to no one.

when doing barrels for a particular chambering, I Take great pains to insure that every one is as identical as my machinist skills will allow.

I have played with various die and press configurations to insure that each round is dimensional straight and correct In all aspects.

But, I am not that great of a shooter in the competitive arena. When not on the clock, things get much better. But for reasons that allude me, I have never been able to mater that technique of putting 5 shots down range in no more time than it takes to cycle the rifle.

In short, I rely on my my equipment, my tuning ability, and choice of components to give me at least a fighting chance when the command of “insert bolts, commence fire” is given.

I have mentored more than one shooter who now beats me in matches on a regular basis, using the exact same things I use.

They are simply better shooters.

 

[nksmfamjp]

Ammunition Demystified

Thanks. Just bought it!

 

[gunsandgunsmithing]

how does group shape change with different lug configurations? if a typical two lug is mounted 90* rotated in a stock do they become biased horizontal? are three lug groups 'naturally' more round? inquiring minds...

Chop, I've never seen a correlation based on 2 lug vs 3 lug actions and the group shapes are virtually always similar. Size may vary from gun to gun and load to load but the shapes are very predictable. As for what happens if the gun is sideways...I've never tried it so I'll just say I don't know but I would assume the groups would keep the same orientation either way.

I post this pic from time to time because it's very representative of what I see and what I look for. It always seems to incite thoughtful discussion so I'll just leave it here too and let you all discuss it. Often our views can be influenced by what we want to be true but testing with an open mind is encouraged.