Barrel harmonic predictor based off of barrel blueprint

[LeftyJason]

Random hypothetical thought. Could you figure out what the barrel harmonics of a specific length barrel of a specific profile is just based off of a barrel print?

Completely made up numbers.
Say you want a 19" medium palma r700 barrel that is threaded 5/8. 6.5 Creed. Could you figure out where the nodes are? Say 2700-2775fps is good as well as 2875-2925fps but not 2800-2850fps or 2625-2675.

I figure it is possible but I don't know or even where to start to figure it out.

Not sure of the utility just random thought.

 

[ShtrRdy]

There are modeling programs which mechanical engineers use but I don't have access to this sort of thing.

Structural Analysis & Simulation Software | Ansys

Solve complex structural engineering problems with Ansys Structural FEA analysis software solution for implicit and explicit structural analysis.

www.ansys.com

 

[MarkLeupold]

Random hypothetical thought. Could you figure out what the barrel harmonics of a specific length barrel of a specific profile is just based off of a barrel print?

Completely made up numbers.
Say you want a 19" medium palma r700 barrel that is threaded 5/8. 6.5 Creed. Could you figure out where the nodes are? Say 2700-2775fps is good as well as 2875-2925fps but not 2800-2850fps or 2625-2675.

I figure it is possible but I don't know or even where to start to figure it out.

Not sure of the utility just random thought.

Well, there's a theory about Optimal Barrel Time (OBT) that makes an attempt at what you're asking. No matter the contour, the harmonic resonance will travel the length of the barrel at the same speed per material. This allows you to predict where the harmonic resonance will be at a specific time. When the vibration wave is at the muzzle or breech (I can't remember which) is the best place for a node. Then it's just figuring out a powder and charge that will put your bullet at the muzzle in that amount of time (programs like Quickload can predict this).

Do some Googleing about OBT and you should get some resources. I'm at work right now and can post good links when I get home if they're needed.

 

[John Glidewell]

I use OBT calculator and Quick load. It has always been very close, within .1 or .2 grains on a load and within .005ms for time almost every time. Only one it did not work was 115 DTACs. I do not use it for anything but a tool to get close and let the shooting tell me the rest of the story.

 

[LeftyJason]

Well, there's a theory about Optimal Barrel Time (OBT) that makes an attempt at what you're asking. No matter the contour, the harmonic resonance will travel the length of the barrel at the same speed per material. This allows you to predict where the harmonic resonance will be at a specific time. When the vibration wave is at the muzzle or breech (I can't remember which) is the best place for a node. Then it's just figuring out a powder and charge that will put your bullet at the muzzle in that amount of time (programs like Quickload can predict this).

Do some Googleing about OBT and you should get some resources. I'm at work right now and can post good links when I get home if they're needed.

Good links would be appreciated. I knew there had to be something out there.

 

[fxdrider]

Good links would be appreciated. I knew there had to be something out there.

Article and links - follow the link below.

Optimum Barrel Time Concept

 

[MarkLeupold]

Good links would be appreciated. I knew there had to be something out there.

Fxdrider has the good link right there ^

That is where you want to start, but I'll see if I can find some more resources for OBT. I remember seeing some good ones over the years

 

[phlegethon]

I am surprised that this can work, given that the trajectory of the bullet must be affected by the deviation of the bore from perfect straightness and that this is different for each barrel. But maybe the harmonics really aren’t affected by that enough.

 

[MarkLeupold]

I am surprised that this can work, given that the trajectory of the bullet must be affected by the deviation of the bore from perfect straightness and that this is different for each barrel. But maybe the harmonics really aren’t affected by that enough.

I would assume it's all accounted for in the static. Barrel whip, at least with target barrels, would be measured in thousands of an inch, not enough for most people to notice the difference of.

https://www.shootingsoftware.com/barrel.htm <- This link I found today talks about barrel whip and the "travelling wave theory." It indicates that you not only want to release the bullet when the travelling wave is near the receiver (ie. far from the muzzle), but also at "full whip," as this will make the bullet release position more consistent across variation (the barrel "lingers" at that spot due to how harmonic waves behave).

An interesting note from that article is the claim that the "travelling wave theory" has been documented using high-speed photography and that if releasing the bullet while the wave is at the muzzle will cause a similar behavior to if the barrel had a bad crown, blowing propellant past/off axis from the bullet, inducing yaw at the muzzle.