What determines the width of an accuracy node?

[jlow]

So this is a question for the real experts. I think we have all seen groups posted on Eric’s thread. The question is what determines the width of an accuracy node? Is it the rifle, the caliber, the load, or a combination of the three?

Post your response but it would be useful if it was backed up with some data.

 

[4xforfun]

I say it is the size of the case. The Nodes on my dashers are 1/2 to 3/4 grain wide. The nodes on my 300 WBYs is 1 1/2 ++ wide.

Of course, on the other hand, as a percentage of case capacity, they are close to the same.

So....never mind

Tod

 

[Alex Wheeler]

I believe it is the design of the rifle, rigidity, location of the center of gravity, position of the bags, exc. Velocity nodes seem to be powder dependent. Rl powders seems to jump every time you add powder, while H powders seem to have nodes where velocity does not change.

 

[jlow]

Interesting! Thanks guys keep it coming in!

I was wondering about the barrel contour. Seems like a thicker barrel should have less flex and tighter harmonics (if there is such a thing) which should make the "degree of fling" ;D less and so the node should appear to be wider?

Speaking of case size - anyone see a 223 node (small case) that is wider than a 1/2 grain?

 

[Alex Wheeler]

Close, the stiffer barrels frequency is higher so the nodes are smaller.

 

[Jay Christopherson]

I believe it is magic.

 

[jlow]

Close, the stiffer barrels frequency is higher so the nodes are smaller.

That makes sense but would the overall fluctuation be smaller due to increase stiffness? That is the reason why I put "appear to be wider" in that post. Kind of falls into the "rigidity" that you posted.

 

[Changeling]

Jay congratulations on your post number 1111, go buy a lottery ticket, LOL.

 

[Brians356]

<subscribe>

Why don't an individual's "Posts" count increment within a thread?

 

[Alex Wheeler]

Close, the stiffer barrels frequency is higher so the nodes are smaller.

That makes sense but would the overall fluctuation be smaller due to increase stiffness? That is the reason why I put "appear to be wider" in that post. Kind of falls into the "rigidity" that you posted.

Yes, the amplitude will be smaller in a heavier barrel. Ever notice how when your out of a node in a pencil barrel the groups are huge, but when your out of a node in a heavy barrel they are still moa-ish?

 

[jlow]

Close, the stiffer barrels frequency is higher so the nodes are smaller.

That makes sense but would the overall fluctuation be smaller due to increase stiffness? That is the reason why I put "appear to be wider" in that post. Kind of falls into the "rigidity" that you posted.

Yes, the amplitude will be smaller in a heavier barrel. Ever notice how when your out of a node in a pencil barrel the groups are huge, but when your out of a node in a heavy barrel they are still moa-ish?

Thanks! Amplitude - that's the word I was looking for... ;D

 

[CatShooter]

Close, the stiffer barrels frequency is higher so the nodes are smaller.

But barrels get stiffer by getting heavier - and the heavier they are, the lower the frequency they vibrate...

... like big bells and tinker bells.

 

[vinny]

I was told a while ago by a recently passed Williamsport H.O.F shooter that "trigger time" answers a lot of questions.
RIP Frank

 

[Sullivan]

I think it's a combination. I shoot a tikka t3 Varmit heavy barrel in .308. I've tried 4 different bullet weights and 6 different powders. I can only make the real magic with specific components. You know the 3 or 4 shots in one hole on a 5 shot group at 200. You can tune anything to shoot just OK. But the real magic only happens when it all works together correctly. They say in hand loading no 2 rifles shoot exactly the same. That's my take on it.

 

[CPorter]

It is a combination of several factors. Harold Vaughn shows this in his book "Rifle Accuracy Facts". You can also look up Varmint Al's website and see the finite element analysis he did on barrels, actions and other things. It shows animations to help you understand. Barrel length, thickness, material, profile, action shape, the number of hole cut into it and their location all change the vibration patterns. The load and bullet are like selecting different mallets to strike a bell.

 

[CatShooter]

The load and bullet are like selecting different mallets to strike a bell.

Badd analogy cuz no matter what you hit the bell with, it rings with the same tone (frequency).

Same with barrels - the barrel vibrates with the same frequency unless you cut it - the reason changing the load improves things (or makes them worse) is that you change the time in the barrel, so you change the exit time in the vibration cycle.

 

[Alex Wheeler]

Close, the stiffer barrels frequency is higher so the nodes are smaller.

But barrels get stiffer by getting heavier - and the heavier they are, the lower the frequency they vibrate...

... like big bells and tinker bells.

Not exactly. Barrels get stiffer by adding weight in the right areas. Straight barrels are heavy but not as stiff as some taper.

 

[CatShooter]

Close, the stiffer barrels frequency is higher so the nodes are smaller.

But barrels get stiffer by getting heavier - and the heavier they are, the lower the frequency they vibrate...

... like big bells and tinker bells.

Not exactly. Barrels get stiffer by adding weight in the right areas. Straight barrels are heavy but not as stiff as some taper.

We will have to agree to disagree - that makes no sense.

 

[Alex Wheeler]

Close, the stiffer barrels frequency is higher so the nodes are smaller.

But barrels get stiffer by getting heavier - and the heavier they are, the lower the frequency they vibrate...

... like big bells and tinker bells.

Not exactly. Barrels get stiffer by adding weight in the right areas. Straight barrels are heavy but not as stiff as some taper.

We will have to agree to disagree - that makes no sense.

http://www.riflebarrels.com/articles/barrel_making/rigidity_benchrest_rifles.htm
Adding weight to the muzzle end does not make the barrel stiffer. Agree to disagree.

OP Varmint Al's web site is an excellent source of good info. Here you will just get opinions (like mine)

 

[CatShooter]

Close, the stiffer barrels frequency is higher so the nodes are smaller.

But barrels get stiffer by getting heavier - and the heavier they are, the lower the frequency they vibrate...

... like big bells and tinker bells.

Not exactly. Barrels get stiffer by adding weight in the right areas. Straight barrels are heavy but not as stiff as some taper.

We will have to agree to disagree - that makes no sense.

http://www.riflebarrels.com/articles/barrel_making/rigidity_benchrest_rifles.htm
Adding weight to the muzzle end does not make the barrel stiffer. Agree to disagree.

OP Varmint Al's web site is an excellent source of good info. Here you will just get opinions (like mine)

Who the hell is talking about adding weight to the muzzle end... in a discussion like this, it should be assumed that we are talking about "normally made" barrels, unless otherwise stated - otherwise we can talk about barrels that have fat sections every 6" along their length and those that are shaped like trumpets

If you are comparing 26" barrels, the heavier one (e.i. the fatter one) that is "normally made, will ring at a lower frequency.

IF you need to go that far off track to "prove a point", you got a real whimpy point.