Does Barrel Vibration Exist and Does it Matter

[Doom]

OK. An ongoing question. A lot of information and misinformation is out there. Yes it matters. The attached link to a Paper by FN covering a redesign of a SAW barrel is probably one of the best that is available that demonstrates the impact.

https://apps.dtic.mil/sti/tr/pdf/ADA434693.pdf

 

[ELR LVR]

Before I go and read 28 pages of something
Easy answer
Yes, barrels vibrate,
it can be easily seen and witnessed with slow mo photography
-------------
Does it matter?
Your target will let you know how much it matters
-------------
It is not a difficult concept to comprehend or even test with a simple hammer
and hanging a u-bolt on the barrel

 

[Doom]

Before I go and read 28 pages of something
Easy answer
Yes, barrels vibrate,
it can be easily seen and witnessed with slow mo photography
-------------
Does it matter?
Your target will let you know how much it matters
-------------
It is not a difficult concept to comprehend or even test with a simple hammer
and hanging a u-bolt on the barrel

Yep. You're right on both counts and there are some test reports on barrel vibration. This is the only small arms analysis that I have seen where it is included in the dispersion analysis.

 

[jelenko]

I found interesting that they lined the barrels with Stellite and coated that with a ceramic coating.

That would be a expensive barrel.

 

[RegionRat]

I found interesting that they lined the barrels with Stellite and coated that with a ceramic coating.

That would be a expensive barrel.

It (Stellite liners and special coatings) was common for bigger weapons even before they tried it for these barrels.

The report makes a few mentions of the work on heavier weapons where they borrow some technology and try to apply it here.

Since the overall program focus was a combination of weight reduction and the material science applications, they really don't publish anything all that informative about the modal analysis, other than to compare a few parameters of their proposed changes to the existing baselines.

If you noticed, their predictions and the actual dispersion results were vastly off, but in reality, their analysis here never was intended to predict the target. It was just to compare some stiffness/stress parameters based on the section changes.

It takes a lot more complex modeling to close loop on ballistic accuracy, velocity, heat, and wear, than what is shown in this report. Those types of report are not public.

If there is a real takeaway point to the report, it is that stress, dynamics, and thermal models of weapon systems were highly dependent on experimental anchoring before the analytic models became useful.

My definition of useful here being the use of the model to avoid more costly prototype and physical lab work, and to drive designs that met performance.

The damping, wear, thermal, and dynamics presented in the report, didn't do a very good job at all. However, the point of the project wasn't to perfect the analysis models.

The use of stress, dynamics, and harmonic analysis for guns and cannons pre-dates the use of FEM or NASTRAN models. I was shocked at how old some of the work that predates the design of Mauser barrels was when I was a student. Those papers were from the 1800's in German.

Do barrel sections affect vibrations and does that matter? Of course, the answer is yes, it matters very much. YMMV

 

[CharlieNC]

The muzzle vibration amplitude is .003 - .005in at the frequency associated with the the speed of sound traversing the the barrel. This is the driver for positive compensation as observed on the target.

 

[Bottom Fodder]

Ok just asking simple questions on the harmonics of barrel as for accuracy
Does a tuner change these harmonics to increase accuracy/ retune a barrel
Does a adjustable pressure point on the forearm that puts pressure on the barrel
Like a Ruger #1 has to change the Harmonic work like a Turner
Would the harmonics of a short heavy barrel be changed less by say a turner or load. Just thinking out loud. Opinions?

 

[jds holler]

I've always wonder what the effect of some of those huge "safari front sights" might have on harmonics. They are often mounted on pencil barreled hunting rifles, and I can't imagine they don't work as a tuner -- or de-tuner. jd

 

[CF Junkie]

Find articles on Optimum Bullet Time (sometimes referred to as Exit Time) that provide information on the way to tune loads to nodes in the vibrations.

I find that the worst to best conditions produces about a 0.090 inch variation in group sizes at 100 yards, (with the same powder, primer, bullet, and brass).

For me, the best condition occurs when the shock wave is at the chamber when the bullet is exiting the muzzle. The worst occurs when the shock wave is at the muzzle when the bullet exits. It not only has the largest vibration but the distortion of the crown is the greatest. At least, that is the theory.
For me is seems to work.

 

[CF Junkie]

Tuners can easily change the harmonics of a barrel.
I am not sure how you might determine the desired adjustment without lots of experimentation.

Using Optimum Bullet Time and correct calculations of barrel length and knowing the reflection speed of the steel in the barrel, I can get to a known Optimum Bullet Time with a new rifle with a few calculations.

It seems to work and I use that approach on 7 of my most accurate target rifles.
I just added two new Shilen barrels, and the results are incredible in the second session - the break-in session was unmeasured.

 

[RegionRat]

Ok just asking simple questions on the harmonics of barrel as for accuracy
Does a tuner change these harmonics to increase accuracy/ retune a barrel
Does a adjustable pressure point on the forearm that puts pressure on the barrel
Like a Ruger #1 has to change the Harmonic work like a Turner
Would the harmonics of a short heavy barrel be changed less by say a turner or load. Just thinking out loud. Opinions?

First, there is no such thing as a "simple question" when it comes to how external and internal ballistics combine with dynamics to affect accuracy.

Entire books have been written and even taken together with all the additional books in their bibliography, barely begin to explain your question.

Does a tuner change these harmonics.... yes, depending on the mass and position they change the frequency, however.... the part of your question about increase accuracy/retune a barrel.... the answer is sometimes yes, and sometimes no. Not every mass will affect the accuracy even if it does affect one or more of the major frequencies.

...Does an adjustable pressure point...... yes, those are very old and proven methods to both re-tune a frequency and more importantly an amplitude. Let's not forget that the way a barrel, action, stock are connected/supported, and any human support, are still the major contributors in the vast majority of designs. Even a change to the bag stiffness (or friction) in a BR or F-Class rig, will affect the tuning and accuracy. Here again, the recoil is a major contributor because the guns start to move before the bullet exits.

Short heavy section bbls have frequencies that are higher because the section stiffness and weight ratio goes in that direction.

If we said the frequency goes roughly by the square root of the stiffness over the mass, and that higher frequency results in lower amplitude, then they can sometimes be more accurate when compared to an equal bore in a longer bbl with a lower section stiffness.

Keep in mind, in a real-world situation where the gun is carry weight, the recoil mode is the largest and affects the accuracy more than all the harmonics from the structural stiffness. Now clamp that same barrel into a shooting machine, and those barrel harmonics will become the greater share of the accuracy. YMMV

 

[ISS]

Barrel = tuning fork.

 

[Bottom Fodder]

Barrel = tuning fork.

I like your simple answer

 

[ELR LVR]

For me, the best condition occurs when the shock wave is at the chamber when the bullet is exiting the muzzle.

The worst occurs when the shock wave is at the muzzle when the bullet exits.

BINGO !!!

 

[jelenko]

I've always wonder what the effect of some of those huge "safari front sights" might have on harmonics. They are often mounted on pencil barreled hunting rifles, and I can't imagine they don't work as a tuner -- or de-tuner. jd

But, don't they take shots at like 50 yards or less?

 

[Chris Edmondson]

It ticked me off to no end back in the MagentoSpeed chronograph days, I'd strap that thing to my 28" fluted X-bolt 6.5 CM barrel and darn it, the group sizes shrank, every time . Of course, there's an equal chance it could've gone the other way.

 

[jds holler]

I've always wonder what the effect of some of those huge "safari front sights" might have on harmonics. They are often mounted on pencil barreled hunting rifles, and I can't imagine they don't work as a tuner -- or de-tuner. jd

But, don't they take shots at like 50 yards or less?

So, my first high power rifle was a Ruger M77 that I bought with high school graduation money back in 1974. The rifle was brand new and cost $176.00. It was a 243 Win, and it had those safari sights which was a good thing because I didn't have enough money to get a scope for a couple months.

So as soon as I could afford it I picked up a Weaver K4, and a Lee Loader with loading supplies. THAT RIFLE WAS A SHOOTER!! I don't know if the safari sights helped, but they sure didn't hurt.
My "whack-a-mole" ammo with powder weighed to the tenth was just fine, and I don't do much better with the ammo I load these days. jd

 

[B Nettesheim]

The idea of wrapping aluminum around a barrel has intrigued me for sometime, I’ve read about it in rimfire sports and figured why not give it a whirl in a centerfire. It was an all day affair to accomplish the wrap the way I wanted to but the results have been good. I wouldn’t give too much credit the wrap because it’s only been tested very little but has won all the matches I shot it in. Another couple barrels this way with similar results would give better data. 300 wsm in f class.

 

[TylerFromMS]

View attachment 1696094
The idea of wrapping aluminum around a barrel has intrigued me for sometime, I’ve read about it in rimfire sports and figured why not give it a whirl in a centerfire. It was an all day affair to accomplish the wrap the way I wanted to but the results have been good. I wouldn’t give too much credit the wrap because it’s only been tested very little but has won all the matches I shot it in. Another couple barrels this way with similar results would give better data. 300 wsm in f class.

This is what I use for my guns. Hope this helps.

Amazon.com: Aluminum Foil Roll 18"x 500 feet (1 Pack) - Aluminum Foil Heavy-Duty, Commercial Grade for Food Service Industry - Silver Foil for Cooking & Roasting : Health & Household

Amazon.com: Aluminum Foil Roll 18"x 500 feet (1 Pack) - Aluminum Foil Heavy-Duty, Commercial Grade for Food Service Industry - Silver Foil for Cooking & Roasting : Health & Household

www.amazon.com

 

[Straightshooter1]

Yep. You're right on both counts and there are some test reports on barrel vibration. This is the only small arms analysis that I have seen where it is included in the dispersion analysis.

What I found particularly interesting was the graphs of the displacement (Figures 7 & 8, pages 23-24 of the file) before and as the bullet leaves the muzzle.