What determines the width of an accuracy node?

[seymour fish]

Zfast, I think based on playing with the PRX tuning method in rimfire personally, and based on the wide acceptance by a large percentage of top flight competitors who seem to find that it often puts them rather immediately within a few clicks of a perfect tune , that there is more going on, at least in this domain, than simple mass effect. No crossover yet into centerfire that I am aware of. The notion of a barrel bulge moving back and forth from action to muzzle often surfaces. I find it enticing, and have found a correlation of about 0.8 between best loads and barrel times using quickload/accrate chrono data/Ba manipulation to standardize the two, and Chris Longs predicted optimum barrel times modified by a 1% fudge factor. Simply a correlation, but a strong one. Seymour

 

[Tim Singleton]

On the width of the node
I don't own anything but LV taper 22" rifles and as I adjust seating depth I see groups form low working up relative to my poa as I adjust the depth.
As much as 1/2" poi change from one depth to another. As ishown Eric's post

Anyone have experience with an unlimited rail gun with a 1.5" straight contour? I wonder if the range the groups form are as far apart as they are with an LV barrel

 

[gunsandgunsmithing]

Mike I would like to hear your opinion as to if you feel the moving bullet in the bore would have an effect on the frequency of the barrel?

Alex, I think it's an interesting notion. I don't disagree as the barrel would be somewhat solid wherever the bullet is, at any point in time, rather than being a tube, but the density within would be different than the barrel itself. That's bound to change the frequency it vibrates at to some degree. That said, I would consider it a constant, in that it does basically the same thing from shot to shot, excluding velocity variations...which are a whole other subject in regard to tuning. A mass moving in or on the barrel won't change the mass of the barrel, but will change the center of that mass. If anything, the total mass would lessen as leaking gasses expel around the bullet. I almost feel the bullet in bore notion is a non-issue because it is a constant, regardless of where it is in the bore at any given nonosecond. Yet, in the interest of learning, I have to admit and be open minded, that it may have more effect than I'm giving credit for.
Hell, I was hoping you'd explain it to me. ;D

 

[gunsandgunsmithing]

On the width of the node
I don't own anything but LV taper 22" rifles and as I adjust seating depth I see groups form low working up relative to my poa as I adjust the depth.
As much as 1/2" poi change from one depth to another

Anyone have experience with an unlimited rail gun with a 1.5" straight contour? I wonder if the range the groups form are as far apart as they are with an LV barrel

Tim, how long are both barrels? At some point, a 1.500 straight is LESS rigid than an shorter lv contour. That's why I try to speak in terms of barrel stiffness in this context. Lilja has a barrel stiffness calculator on his site. Muzzle deflection may be yet a better term for describing barrel stiffness.
Obviously, your seating depth changes are changing bullet exit time in relation to muzzle location.

 

[Tim Singleton]

On the width of the node
I don't own anything but LV taper 22" rifles and as I adjust seating depth I see groups form low working up relative to my poa as I adjust the depth.
As much as 1/2" poi change from one depth to another

Anyone have experience with an unlimited rail gun with a 1.5" straight contour? I wonder if the range the groups form are as far apart as they are with an LV barrel

Tim, how long are both barrels? At some point, a 1.500 straight is LESS rigid than an shorter lv contour. That's why I try to speak in terms of barrel stiffness in this context. Lilja has a barrel stiffness calculator on his site. Muzzle deflection may be yet a better term for describing barrel stiffness.
Obviously, your seating depth changes are changing bullet exit time in relation to muzzle location.

Both barrels at 22 inches. I just wondered if a larger OD barrel of the same length offered smaller muzzle location swing. I've never shot or tuned an unlimited rail. They may have just as much poi change from group to group as an LV I don't know
It would seem if they don't deflect as much, then the poi for groups would be closer together as you adjust seating depth. Would one call this a wide tuning node? Or a small tuning node?

 

[gunsandgunsmithing]

On the width of the node
I don't own anything but LV taper 22" rifles and as I adjust seating depth I see groups form low working up relative to my poa as I adjust the depth.
As much as 1/2" poi change from one depth to another

Anyone have experience with an unlimited rail gun with a 1.5" straight contour? I wonder if the range the groups form are as far apart as they are with an LV barrel

Tim, how long are both barrels? At some point, a 1.500 straight is LESS rigid than an shorter lv contour. That's why I try to speak in terms of barrel stiffness in this context. Lilja has a barrel stiffness calculator on his site. Muzzle deflection may be yet a better term for describing barrel stiffness.
Obviously, your seating depth changes are changing bullet exit time in relation to muzzle location.

Both barrels at 22 inches. I just wondered if a larger OD barrel of the same length offered smaller muzzle location swing. I've never shot or tuned an unlimited rail. They may have just as much poi change from group to group as an LV I don't know
It would seem if they don't deflect as much, then the poi for groups would be closer together as you adjust seating depth. Would one call this a wide tuning node? Or a small tuning node?

Tim, I think you're on subject, as this thread seems to be covering a lot of ground. There's probably room for about 50 threads on the specific areas covered in this one.
Hopefully, my tuner testing will help build a plot around this subject. I feel it has to be specific to relative barrel stiffness. I hope to be able to build a chart that approximates ideal weights and locations for barrels of specific stiffness factors. Even if it can be precisely determined for a specific barrel stiffness, there are still lots of variables, such as stocks and rests, and overall dampening of the entire package as it's sets on the bench....which may itself, be of value.
I feel that a stiffer barrel offers a narrower tune window but an overall reduced muzzle displacement,. So, a rail gun may shoot respectably well, even when out of tune. Tuners place dominance of oscillation on the vertical plane, so regardless of stiffness, vertical is the main component, but certainly not, as some claim, the only component. By increasing the amount, or amplitude of muzzle displacement on the vertical plane, the frequency seems to lower, even though, frequency and amplitude are independent of one another. This is, IMO, due to the added mass of the tuner as well. So, even though the two are independent, they are both affected by added mass at the muzzle.
Bottom line, a more flexible barrel/gun will have a wider tune window, but it may be more an issue of percentage of muzzle displacement that we are really after. That's where I believe a more efficient dampener(tuner) is of value.

 

[gunsandgunsmithing]

It's time for some college basketball. You boys from Texas better go grab a stiff drink.

 

[Alex Wheeler]

On the width of the node
I don't own anything but LV taper 22" rifles and as I adjust seating depth I see groups form low working up relative to my poa as I adjust the depth.
As much as 1/2" poi change from one depth to another

Anyone have experience with an unlimited rail gun with a 1.5" straight contour? I wonder if the range the groups form are as far apart as they are with an LV barrel

Tim, how long are both barrels? At some point, a 1.500 straight is LESS rigid than an shorter lv contour. That's why I try to speak in terms of barrel stiffness in this context. Lilja has a barrel stiffness calculator on his site. Muzzle deflection may be yet a better term for describing barrel stiffness.
Obviously, your seating depth changes are changing bullet exit time in relation to muzzle location.

Both barrels at 22 inches. I just wondered if a larger OD barrel of the same length offered smaller muzzle location swing. I've never shot or tuned an unlimited rail. They may have just as much poi change from group to group as an LV I don't know
It would seem if they don't deflect as much, then the poi for groups would be closer together as you adjust seating depth. Would one call this a wide tuning node? Or a small tuning node?

Tim, I think you're on subject, as this thread seems to be covering a lot of ground. There's probably room for about 50 threads on the specific areas covered in this one.
Hopefully, my tuner testing will help build a plot around this subject. I feel it has to be specific to relative barrel stiffness. I hope to be able to build a chart that approximates ideal weights and locations for barrels of specific stiffness factors. Even if it can be precisely determined for a specific barrel stiffness, there are still lots of variables, such as stocks and rests, and overall dampening of the entire package as it's sets on the bench....which may itself, be of value.
I feel that a stiffer barrel offers a narrower tune window but an overall reduced muzzle displacement,. So, a rail gun may shoot respectably well, even when out of tune. Tuners place dominance of oscillation on the vertical plane, so regardless of stiffness, vertical is the main component, but certainly not, as some claim, the only component. By increasing the amount, or amplitude of muzzle displacement on the vertical plane, the frequency seems to lower, even though, frequency and amplitude are independent of one another. This is, IMO, due to the added mass of the tuner as well. So, even though the two are independent, they are both affected by added mass at the muzzle.
Bottom line, a more flexible barrel/gun will have a wider tune window, but it may be more an issue of percentage of muzzle displacement that we are really after. That's where I believe a more efficient dampener(tuner) is of value.

Great post especially the bold part. Everyone wants to stiffen everything up. Wrong direction
Its fun to talk about, but until someone with some serious money comes along we'll never really know what is happening. But we all are entitled to our own theories.

 

[Alex Wheeler]

I also believe the center of gravity of the rifle has a huge effect on how the gun will shoot, and is a overlooked aspect of building a rifle.

 

[Jason Boersma]

The balance point? Or how low it rides in the bags?

 

[Alex Wheeler]

Neither. The rifles's center of gravity.

 

[Tim Singleton]

For my use anyway. I'm looking for a seating depth and tune that has the smallest amount of vertical separation between test groups with different powder charges
So a more flexible barrel would be working against what I'm looking for to begin with
as Eric describes in his thread I look for groups that have different powder charges to form in the same place vertically on the target. This is done with seating depth adjustments or a tuner
The gun is in Tune when groups with different powder charges form at the same place or as close as possible to the same place vertically on the target. So I would think a barrel that was stiffer would offer a better start at this process
So does the barrel stiffness define the accuracy node the OP asks. No I don't think so. but i think it's a major factor

 

[savagedasher]

I also believe the center of gravity of the rifle has a huge effect on how the gun will shoot, and is a overlooked aspect of building a rifle.

CG height and balance point has always had effect on tune. I have watch muzzle loader shoot with the barrel only setting on the front bag. I had a short fore end stock with a long heavy barrel that I shoot with the barrel on the bag. Thinking back it shot better off the barrel then it did in the stock.
Larry

 

[Alex Wheeler]

For my use anyway. I'm looking for a seating depth and tune that has the smallest amount of vertical separation between test groups with different powder charges
So a more flexible barrel would be working against what I'm looking for to begin with
as Eric describes in his thread I look for groups that have different powder charges to form in the same place vertically on the target. This is done with seating depth adjustments or a tuner
The gun is in Tune when groups with different powder charges form at the same place or as close as possible to the same place vertically on the target. So I would think a barrel that was stiffer would offer a better start at this process
So does the barrel stiffness define the accuracy node the OP asks. No I don't think so. but i think it's a major factor

You are looking at it wrong. The OCW method and ladder testing do the same thing. You are looking for a spot where multiple loads hit the same poi. The stiffer the barrel the smaller the amplitude and higher the frequency will be, which will narrow the node and cause there to be less groups at the same poi. At the extreme, an ultra stiff barrel would be un tunable because there would not be enough dwell time in each cycle to allow for the slight variations in our ammo to still hit the same poi. At the other end is the pencil barrel that suffers for extreme amplitude and heat. There is a happy medium. But the "common knowledge " is stiffer=better, and thats flat wrong IMO.

 

[savagedasher]

I have 3 Dashers 2 with 1.250 straight barrels the 3 has 119.0 Straight taper. Chambered alike.
QL has a barrel time listed for 29'' 30'' and 32''
Gun 1 29'' has a barrel time of 1.257
Gun 2 30'' has a barrel time of 1.284
gun 3 32'' 1.337
With 3 different Barrel times using the same load in each. With the RAS tuner break I can make them shoot .125 or less with a fast tune. The gun I'm shooting if the if the conditions are good and I do my thing right it will shoot .100 or less.
A friend of mine that I shoot with was shooting a varget load and it had a 1/2 ''of 45 degree vertical horizontal pattern. He as changing powder drop and seating depth. I took my tuner brake off my gun and put it on his. With no changes it shot.250 or less. With a very small change it tuned to .200 and less.
He handed me $180.00and I never got it back.
Barrel time to me is not something I worry about . Larry

 

[seymour fish]

Ssavage, Are the barrel times you list based on backfeeding chronograph data into Quickload to dial in the Ba ?; or based on quickload estimates based on bbl length/case capacity (default setting vs actual measured)/default powder Ba? Did the short-range improvement hold up at 600-1000 ? If so, I'm going back to throwing charges and get a tuner ! Seymour

 

[savagedasher]

Ssavage, Are the barrel times you list based on backfeeding chronograph data into Quickload to dial in the Ba ?; or based on quickload estimates based on bbl length/case capacity (default setting vs actual measured)/default powder Ba? Did the short-range improvement hold up at 600-1000 ? If so, I'm going back to throwing charges and get a tuner ! Seymour

The load I used was with in 5 FPS of QL with the 30'' barrel.
I have changed powder types. with as much as 150' fps difference with the same results.
At 600yd I shot 1.065 and1.652 Before the wind changed.
My ES are around 3 .That didn't happen till I sorted the cases by H20 capacity.
DR ED who took the one off my gun has got two more with the same results
If you go to Bostrom Gunsmithing you can see the results. We will have more data in a few weeks.
Larry

 

[gunsandgunsmithing]

On the subject of tune, most of us will agree that our rifles will shoot differently when held or pinned against the rest stop vs. free recoiled. How many of us think about that being physically tune related?

 

[GSPV]

just to throw another dog into the ring-what would happen when a rifle was fired in a vacuum[if this is possible] would the harmonics etc remain .
the reason i ask is i watched an intresting programme on tv about testing in a huge vaccum chamber -as the chamber had near to zero gravity.amazing

Vacuum is an absence of atmospheric pressure. Gravity is something else altogether.

You can think of gravity as a property of mass...the attraction that mass has for mass. There are more complex ideas, but that's an easy way to think of it.

 

[4xforfun]

Exactly Mike

Though it has nothing to do with a barrel…. when I change the strings on my guitar to a heavier gauge string, the sustain [vibration] lasts much longer.

The heavier string must have a higher BC! ;D