There is incontrovertible proof that those who talk about barrel harmonics do not know what they’re talking about, and that proof is in the very term they use to talk about it.
First; the term “harmonic” is a very specific term for an integral multiple of a fundamental vibration frequency. Since a barrel is (usually) a somewhat irregular object tethered at one end, I question whether most of them have a harmonic overtone series at all (like a guitar string or the air column inside a flute) or a primarily inharmonic one, like a bell or a cymbal. “You keep using that word…”
Second; the fundamental frequency of the “resonating” barrel is being ignored (by the language at least) yet the fundamental is often, or probably, more significant, i.e. it probably has a higher amplitude than the higher frequency vibrations. That’s usually very much the case with a vibrating body unless it’s being dampened at the fundamental. So why, particularly, are we discussing overtones (harmonic ones or inharmonic ones) and not the fundamental?
Third; don’t even talk to me about barrel harmonics, or barrel fundamental vibration, or inharmonic barrel overtones (A.K.A. “partials”) on an AK or a 30 Carbine, et al barrel. Just don’t.
I once had to do this with a class of music majors during a seminar I did at the U of Idaho. We were talking about advanced tweaks, the last one percent, of what goes into the design and structure of a musical instrument to make it a really fine one, and the students were responding as though I were talking about major issues. My fault. I should have been more clear at the outset.
So here it is; you don’t address the last one percent on your AK. It’s not a beanfield rifle. Please. There are several other factors that totally overwhelm the last one percent (like the previous 99 for example) and so if you address the last one percent as though it were “the issue” you’re ignoring the issues that matter.
In other words, don’t worry about the last 1% of fine-tuning until you’re past the first 99%. That should be painfully obvious.
Also, some guns will simply never, no matter how much they are tuned, get past that first 99%. Fretting about the last 1% in those cases is pointless.
And yet, it’s it’s amazing how often the painfully obvious become painful only because it wasn’t so obvious sooner. Been there, went “D’oh!” about that.
Considering most shooters can’t get past their first 90%, attempting to squeeze the last 1% from their guns doesn’t really compute a very rational answer. But it can still be fun to try :-).
“But it can still be fun to try”
Oh absolutely, and go for it. It’s the guy who calls me up, deeply concerned about the 1% and nothing else, who I’m addressing (and those who don’t know basic physics terminology but use it anyway).
If I showed you some of my early projects, and told you what I was thinking, you’d probably laugh. Certainly I would be the subject of blistering, scarcastic ridicule in places like arfcom. But if I’d listened to my good friends who cared about my financial well-being I’d never have done what I did for a living for the last 14 years or so because they’d have convinced me it was impossible and stupid (like Progressives try to do to everyone).
Heck yeah; you want to use a Dremel to flute your rifle barrel, go for it, or use epoxy to attach a scope mount, go for it, or put adjustable weights on the muzzle, why not?
I don’t need to tell you what works because you’re in the process of finding out first-hand, which is the best way so long as you keep that hand.
And then there are basic physics (and very basic and very specific meanings of certain words like “harmonic”) which I’ve come to realize a lot of people don’t beleive when they hear about it because their intuition (or something) tells them otherwise. So in that sense I’m pissing in the wind no matter how you look at it. It’s just that people should be given a chance, so I have to try to define “harmonic” when everyone I hear using the word seems not to know what it means.
I guess if anyone wanted to know they could look it up for themselves in about two seconds, so again; piss, wind.
Just so I understand what is being meant…
Is the purpose of tuning the harmonics of the barrel so that the barrel is sitting in the center between the peaks and troughs of the wave-form of the barrel? Wave form prolly isn’t the right word. Or is it getting the barrel to be flexing to the same spot every time on bullet exit?
You want the barrel to be as close to stationary as possible when the bullet exits. For a sine wave vibration in a barrel (dream on!) This means a “trough” or a “peak”. Midway on a sine wave is maximum velocity.
And the forwardmost node in a vibrating bar, such as a xylophone bar or the tine of a tuning fork (and again, dream on) is well back from the end, which means there will be a lot of motion at the muzzle;
http://en.wikipedia.org/wiki/Node_(physics)
The moving graphic on the top right shows what a guitar string harmonic would look like slowed down, as opposed to a bar with a free end.
Again though, there is probably more armchair theory here than practical reality, and we’re talking about final tweaks to an already fine rifle having a free-floated barrel. You start touching spots on the barrel, or pressing other parts onto it, and so on, or heating said assembly from the inside by a couple hundred degrees, and everything changes in complicated ways.
And yet again; we aren’t so concerned about harmonics, I wouldn’t think (assuming a profiled barrel even has significant harmonics at all as opposed to a fundamental and it’s inharmonics) as we are concerned about the fundamental vibrations in discussing this theoretical, final tweak to an already very fine rifle.
So many millions of words have been written on this subject that the instant you start talking about any accessory that touches the barrel of even the lowliest combat carbine, and the first thing that pops into people’s minds, in what can only be described as Pavlovian fashion, is “Barrel harmonics! Wraawk! Barrel harmonics!” Soon we’ll be hearing about the all-important aspects of barrel “harmonics” in pocket pistols unless someone puts a stop to it, which is what I’m trying to do.
Just for science, you can locate the nodes back from the ends of a vibrating bar by holding or supporting it at various points until it vibrates and sustains most freely when you hit it. When it does that, the point where you’re supporting it is the node, or point of least motion. The point of contact which results in the very least resonance (greatest dampening) when you hit it is at an antinode. So I guess you set up your very fine barreled action like it’s a marimba bar and find the anti nodes. Then if something like a stock forend is going to touch the barrel, have it touch at an anti node. Maybe THEN you can concern yourself with harmonics, because dampening a bar or string at an anti node will kill the fundamental and let only the upper partials (harmonic or inharmonic such as they may be) ring out (at some reduced amplitude). Now pressurize the bore with fifty thousand psi and put a super sonic moving piston inside it, and constantly and rapidly change the temperature by hundreds of degrees and see how everything has changed, making your experiment moot.
My experience is that most people who talk about “harmonics” are fanboys of the AR platform.
Seeing as there are only two points of contact between the lower receiver and the upper receiver, and the system has its infamous “wobble” along that joint, you can see how “harmonics” could appear to have an outsized importance to them.
Also, it’s nice to have a readily-available “mystical” reason as to why you missed your target.
Hey; I’m an AR fan boy, or I own several of them so I must be…
Hell, I tend to emphasize free floating barrels on ARs for a very simple reason, having NOTHING to do with “harmonics”. I’ve seen the shift in POI between a tight sling (using the bottom swivel on the FSH), a tight sling (using a sling swivel mounted on the side of the FSH), a barrel mounted bipod, and no sling tension or bipod.
Which is why I want my hold point (whether hand only, tight sling, or bipod) to be something NOT attached to the barrel.
Harmonics? Um, no — the barrel friggin’ bends a slight (but noticeable) amount, especially with a light barrel. If I’m cranking down on a FF tube of some sort, I’m not applying that pressure directly to the barrel, so it should still shoot pretty much the same way, regardless of what I’m doing.
I doubt if barrel whip amounts to even a 1% loss in accuracy. If you diagrammed the things which cause a loss of accuracy, they would be inclusive circles. That tiny flyspeck inside the smallest circle would be barrel whip. This is how my Mizzou rifle coach put it 50 years ago, anyway.
check out http://www.youtube.com/watch?v=ozyw84Swmb4
You can see the barrel whip in the video. You can also clearly see that it barely moves before the bullet leaves, and the moment of greatest deflection happens long after the bullet is gone.
I have lot more I could say on the issue, but if you care to know you will look it up yourself, and if you do not care to know nothing I can say will change that. But in the interest of giving a leg up to those who do want to know:
1. Bull barrels are more useful for their resistance to temperature changes than for their “better harmonics”
2. Stiffer barrels are good, but you will see more effect from longer barrels/slower rounds than in shorter barrels/faster rounds. This is still in the realm of “the last 1%” tough, so worrying about a barrel that does not warp as much when hot is far more important (last 5-10% depending on the gun I would guess).
3. Adding weights to the end of a barrel makes them functionally stiffer (by increasing their mass and moment of inertia) and could be “significant” in a more flexible barrel with a slow round, but a.) this has nothing to do with harmonics of any kind and b.) if you have a barrel that flexes that much you need a different barrel (for target shooting, for anything else the weight of the barrel is probably far more important than getting the last .1 MOA from the bench). The super adjustable “harmonic weights” are crap. A roll of quarters (or 2) ducktaped to the end would do the same thing. In the vast majority of cases they do nothing whatsoever, as referenced in the above video.
For anyone new to precision shooting, the most important factor is how your round is chambered (is it the *exact* same way every time, with the *exact* same weight and diameter bullet, with the *exact* same charge?). Tight tolerances will get you much farther than any form of “barrel tuning”. If you do get to the point where barrel tuning could make a difference (last 1% and all), please understand what you are trying to do (keep the barrel from flexing before the bullet leaves) and tackle that problem in an intelligent way (stiffer barrel, rather than barrel weights for example).
I guess I wound up saying more than I intended, hope it helps. . . .
So Browning’s BOSS was all about the last 1%?
It’s a relief to read of someone affirming my decision to keep my money for that in my pocket. Whatever else I spent it on lo these many years ago now, I’m sure I enjoyed it much more than I would have shooting box after box of some expensive hunting cartridge from a bench while endlessly fiddling with that lump on the end of the rifle.
But it’s SHINY!
As one who admits that I shoot worse than my guns, even my venerable rusted out Mosin Nagant, I have read about barrel harmonics and thought it interesting philosophically but unimportant, or at least insignificant compared to the shooter’s interaction with the rifle.
The “harmonics” should not change much shot to shot if your barrel is warm, or cooled between shots, and relatively clean, because the barrel is a piece of metal, the same each shot, while there is a highly variable meatsack controlling the firearm hold and aim and trigger pull.
This meatsack will worry about harmonics only if shooting a gun mounted securely in a fixed position rest.
Well, ignoring harmonics and talking about barrel flexing instead, the metal stiffness and size does change with temperature, and since we’re talking about millisecond order phenomena, it could matter to some degree at least.
Anyone who works with musical instruments will tell you that temperature is always a concern when it comes to a resonating frequency. Sympnonies have the more aggrivating problem of opposite tendancies– the winds, having an air column as the resonating body, will go sharp as the room and instruments warm up and the air columns become less dense, whereas the strings will go flat as their fixed masses expand and lose tension. They always tune up again after intermission, with the oboe (about the hardest instrument to tune and making the one of most cutting sounds) giving the reference “A”.
Playing outdoors in cold weather can be a nightmare, as the horns go extremely flat with the heavy air inside them.
A gun barrel will not be immune to these principles, so your 1% will be shifting all over the place.