Relationship between bullets weight and barrel harmonics

[Evil_Dark]

Hi everyone,
Is there a correlation between a heavier bullet and the node lenght in the barrel harmonics?

I.E.: A heavier bullet have a shorter node lenght, and lighter bullet tend to have a longer node? (A heavier bullet will create a bigger "wave" in the barrel than a lighter one, right?)

Is this make sense?

I've found multiples nodes with load developpment with 4-5 differents bullets weight, from 140gr to 178gr in my 308win (savage 10TR 5R bull barrel). But now I am trying to find a good node with some Hornady's 208gr ELD, and I found good loads with low StdDev, ( between 6 and 10), but tight groups are very hard to find. I have some at 1MOA, but i do 1/2MOA with 168gr and 178gr, so I am searching a better one, and I can't explain why the node is so hard to find with this bullet. I want hard to have a good load with this bullet, as it will be my long range bullet for 1000+yards. I use IMR-4895 with all my bullets and load.

Thanks!

Dark

 

[J996]

If i may make a suggestion, try some Sierra and Lapua bullets. I never found hornady bullets performed all that great. Sierra and Lapua pills just shoot better for me.

 

[Evil_Dark]

If i may make a suggestion, try some Sierra and Lapua bullets. I never found hornady bullets performed all that great. Sierra and Lapua pills just shoot better for me.

Well, from my experience, Hornady 168gr BTHP Match and 178gr A-MAX are super performer in my rifle, and Sierra Match 168gr are doint a tad less well. I had very good experience with Nosler bullets too, so I can't tag any conclusion based on brands unikely.

Anyway, my question was about the bullet weight and barrel harmonics, not on bullet shape or brand.

Dark

 

[J996]

Well, from my experience, Hornady 168gr BTHP Match and 178gr A-MAX are super performer in my rifle, and Sierra Match 168gr are doint a tad less well. I had very good experience with Nosler bullets too, so I can't tag any conclusion based on brands unikely.

Anyway, my question was about the bullet weight and barrel harmonics, not on bullet shape or brand.

Dark

Ok. The most likely reason is your powder choice for the 208. IMR 4895 is a faster powder and is generally not used for bullets over 200 grains. I would buy some different powders (1 lbs containers) to try with. Try RL15, IMR4064 or Varget. These are what hornady recommend in their cartridge handbook. If you get nowhere with that, its time to switch bullets.

As long as you have a 1/10 twist heavy barrel this should not be a problem. And no I don't think barrel harmonics are the issue

]

 

[Deltasilver]

Hey,

You might want to look at changing powder. I love IMR 4895 but I was never able to make it work with anything heavier than 175gn, not only were the nodes short but it was hard on cases as I got closer to the max.

I had better luck with Varget or the Vihtavouri powders. 43gn of N540 behind a 185gn Juggernaut ran right at 2750 with low SD. Didn't stretch pockets or leave extractor marks either.

��

Lol a minute too slow! What J said. According to the book, the difference in case pressure between a full boat of IMR 4895 and Varget is 10,000psi!

 

[Mystic Precision]

Hi everyone,
Is there a correlation between a heavier bullet and the node lenght in the barrel harmonics?

I.E.: A heavier bullet have a shorter node lenght, and lighter bullet tend to have a longer node? (A heavier bullet will create a bigger "wave" in the barrel than a lighter one, right?)

Is this make sense?

I've found multiples nodes with load developpment with 4-5 differents bullets weight, from 140gr to 178gr in my 308win (savage 10TR 5R bull barrel). But now I am trying to find a good node with some Hornady's 208gr ELD, and I found good loads with low StdDev, ( between 6 and 10), but tight groups are very hard to find. I have some at 1MOA, but i do 1/2MOA with 168gr and 178gr, so I am searching a better one, and I can't explain why the node is so hard to find with this bullet. I want hard to have a good load with this bullet, as it will be my long range bullet for 1000+yards. I use IMR-4895 with all my bullets and load.

Thanks!

Dark

RECOIL... it is harder to shoot more recoil as precisely as less recoil. maybe as simple as a bad rest set up?????

Change powder... H4350 or at least Varget

Different bullet - why does 1 barrel like this vs that... who knows... feed it what it likes. Sierra 210mk, Berger 210gr VLD or BT - maybe that is all there is to the question?

Twist rate... what is the true twist in your barrel????

Why not the 185gr Juggernaut? why not just shoot the 178gr as far as you want to go?

On the up side, components these days are really made well. There are very few choices that can't perform at 1/2 moa or better. Why it may not work in a certain set up... that is a mystery we aren't likely to ever answer.

If you have to fight to get something to work, just change to something else. There are no shortage of really good options.

Simplify...

Jerry

 

[cosmic]

OP - The barrel harmonics (modes, waveforms, and frequencies) are determined by the barrel and action/stock. The varying bullet weights cause a different residence time in the barrel , causing the bullet to exit the barrel at different points in the oscillation cycle. There are better times and worse times, as far as accuracy is concerned...

 

[Evil_Dark]

Thanks for your inputs. I looked on a burning rate chart, and I have one lb of IMR-4350 which is slower than the IMR-4895, so it may improve my results... I will have to remake a ladder test or a OCW.

Thanks!

 

[Evil_Dark]

HOLY COW! The IMR-4350 have not a huge load data for the .308win, as it looks like a too slow burning rate for the usual lighter .308win bullets. As it may be ok for heavier bullets like the 208gr, I didn't found any load on the net.

I probally have to purchase another type of powder...

Dark

 

[J996]

HOLY COW! The IMR-4350 have not a huge load data for the .308win, as it looks like a too slow burning rate for the usual lighter .308win bullets. As it may be ok for heavier bullets like the 208gr, I didn't found any load on the net.

I probally have to purchase another type of powder...

Dark

From Hornady's handbook, 9th edition.

 

[honz]

My understanding is that the node is based on the shockwave velocity from the explosion at the given barrel length, as such - different powders will produce different nodal times.

Now it's about timing the bullet's exit from the barrel with an outgoing node where the heavier bullet will reach the exit slower than a lighter one.

If I am wrong, my ears are perked up to learn.

 

[cosmic]

Honz - I don't have a clue as to what you are saying in your post. For one, the burning of gun powder is a deflagration, not a detonation.
If you want to bone up on the theory of vibration go to Varmint Al's website. He's a mech engineer, just like me, and he's got the time to explain things...

 

[BadAsMo]

Its interesting how frequently people will reference accurate velocity nodes for a certain bullet without mention of the barrel twist rate.

Every decent bullet can be accurate at wildly different velocities if the barrel twist rate is appropriate for the velocity.

If you were to find that a load had to be extremely hot to get good accuracy out of a certain barrel, that would suggest to me that your barrel twist rate is too slow for the bullet you are shooting. At this point you could either re-chamber the rifle to a case with more capacity so you can hit the needed velocity or change to a new barrel with a slightly faster twist rate. Or the obvious choice is to select a shorter bullet.

 

[skypilot]

My understanding is that the node is based on the shockwave velocity from the explosion at the given barrel length, as such - different powders will produce different nodal times.

Now it's about timing the bullet's exit from the barrel with an outgoing node where the heavier bullet will reach the exit slower than a lighter one.

If I am wrong, my ears are perked up to learn.

I tend to agree with a shockwave propagating along the barrel contributing to the axial and radial movement of the barrel and the subsequent node.

I don't believe bullet weight is the initial contributer to nodes as we know them in this context.

Academically, it would seem one could look at barrel timing in milliseconds for optimum barrel timing and simply choose a powder and charge weight that would insure a bullet exit at that timing.

 

[BCBRAD]

My understanding is that the node is based on the shockwave velocity from the explosion at the given barrel length, as such - different powders will produce different nodal times.

Now it's about timing the bullet's exit from the barrel with an outgoing node where the heavier bullet will reach the exit slower than a lighter one.

If I am wrong, my ears are perked up to learn.

My understanding is, the shock wave travels at 19,000 to 20,000 ft/s depending if it stainless steel or carbon steel.

Knowing that, refer to this chart https://docs.google.com/viewer?url=http://www.the-long-family.com/OBT%20Table.pdf What you are trying to do is have the bullet exit on a node (where the barrel is the smallest diameter). The chart denotes times at 1" intervals.

Another thing is the powder (dispensed to +/0 0.02 grains) should have all the deterrent chemicals,Z1, burnt at max chamber pressure Pmax, this will lower the ES, all things being equal.

Heavier bullets will be lower in velocity to lighter ones, so will take longer to get to the end of the barrel.

 

[Ron AKA]

My understanding is that the node is based on the shockwave velocity from the explosion at the given barrel length, as such - different powders will produce different nodal times. Now it's about timing the bullet's exit from the barrel with an outgoing node where the heavier bullet will reach the exit slower than a lighter one.

If I am wrong, my ears are perked up to learn.

You are partly right. A "node" or "sweet spot" is when the bullet exits the barrel when the barrel is vibrating on the upward cycle. Some would say toward the end of an upward cycle, but still the upward cycle. You are not looking to have the bullet exit when the barrel is stopped. When the bullet exits on an upward cycle a slow bullet exits late and when the barrel is pointing higher. This compensates for the lower velocity. A fast bullet exits sooner when the barrel is pointed lower and makes up for the higher velocity. This self compensating effect is what creates the sweet spot. That is why when you do a ladder test you increase velocity but POI does not elevate in the sweet spot.

To the OP's question, for sure a heavy bullet will need a new sweet spot. It is not because the bullet is heavy, it is because the bullet is slower and has a later exit time. If you had a sweet spot velocity for a lighter bullet, it would probably work fine for the heavy bullet, except for the fact that you likely cannot safely put enough powder in the case to get the heavy bullet to that velocity.

In my view nodes or sweet spots have everything to do with the barrel length, weight, profile, and most importantly bullet velocity, and very little to do with things like the powder used. A chronograph, and a ladder test is the fastest way to find the sweet spot velocity.

 

[Ron AKA]

My understanding is, the shock wave travels at 19,000 to 20,000 ft/s depending if it stainless steel or carbon steel.

Knowing that, refer to this chart https://docs.google.com/viewer?url=http://www.the-long-family.com/OBT%20Table.pdf What you are trying to do is have the bullet exit on a node (where the barrel is the smallest diameter). The chart denotes times at 1" intervals.

Another thing is the powder (dispensed to +/0 0.02 grains) should have all the deterrent chemicals,Z1, burnt at max chamber pressure Pmax, this will lower the ES, all things being equal.

That is the "theory" being spread by those who make the computer program that makes such predictions. I don't believe it. Varmint Al is on the right track with barrel vibration, and barrel position at bullet exit.

 

[Evil_Dark]

In fact, I adopted all the theories and the Ladder test. but now that I've done the ladder test, and read the results to apply the given sweet spot, It fail to give a tight group. I can achieve a low SD and ES velocities, but the bullets are hitting all over the target (as much as 6 inches wide at 200Y, on a rifle capable of sub MOA). Here's the FPS results of the first ladder test and the subsequent "fine tunning" tests.

I know that the latest loads were exceeding the max suggested loads in the books, but I've got no signs of overpressure on the brass.
The only accpetable group was with the 39.8gr load, there were 3 shot touching each others, and two flyers two inches apart. Again, the rifle is making nice groups with other bullets right after so the mounts, scope and action are removed from the issue.
I noticed a huge increase of velocity from the first 3 shots group at 39.8gr and the 5 shot groups made the second time (3rd image), alomost 100fps more. I have to find out why.

Funny also that a lower powder charge is giving higher velocities and a huge spread!

Dark

 

[Ron AKA]

How have you done the ladder test? The only way to get meaningful results is to plot the vertical vs the velocity, and look for flat spots where velocity goes up but vertical does not. The purpose of the ladder test is to identify a sweet spot velocity. Have you done that? As long as you track the velocity of each shot and match it to the vertical point of impact, having high standard deviation of velocity is not a problem. All you are trying to do is determine your sweet spot velocity. Worry about standard deviation later.

According to Hodgdon 41 grains of IMR4895 is the maximum load. That is probably why your loads over 41 grains are giving you messed up velocities. You are overpressure.

And back to your original question the points of issue are your barrel length, which I presume has not changed. The bullet weight does not change the sweet spots. What it changes is your maximum velocity. For example if you identified a sweet spot at 2700 fps with a 168 grain bullet, that is interesting to know, but not helpful when you shoot a 208 grain bullet. You can't get velocity to that point with the heavier bullet. Now you need to find another sweet spot in the 2400-2600 fps range.

 

[Evil_Dark]

How have you done the ladder test? The only way to get meaningful results is to plot the vertical vs the velocity, and look for flat spots where velocity goes up but vertical does not. The purpose of the ladder test is to identify a sweet spot velocity. Have you done that? As long as you track the velocity of each shot and match it to the vertical point of impact, having high standard deviation of velocity is not a problem. All you are trying to do is determine your sweet spot velocity. Worry about standard deviation later.

According to Hodgdon 41 grains of IMR4895 is the maximum load. That is probably why your loads over 41 grains are giving you messed up velocities. You are overpressure.

And back to your original question the points of issue are your barrel length, which I presume has not changed. The bullet weight does not change the sweet spots. What it changes is your maximum velocity. For example if you identified a sweet spot at 2700 fps with a 168 grain bullet, that is interesting to know, but not helpful when you shoot a 208 grain bullet. You can't get velocity to that point with the heavier bullet. Now you need to find another sweet spot in the 2400-2600 fps range.

So you mean that the barrel "wave" is the same regardless of the bullet weight/type? Interesting. I was thinking that the wave of the barrel has a different amplitude if the bullet is heavier, because the peak of the pressure will be different (higher on the case of a heavier bullet).

Dark