this physicist (don't glaze over yet) has a plain english, simple benchtop experimental explanation for much of what happens when applying an impulse to a 'hard' piece of steel... there are a couple of hidden gems in his video... among them the statement at about 19:25. For me it was well worth the 20 minutes to watch this. Hope this helps at least someone trying to get their head around the complexity of tuning.
Barrel harmonics in plain english
- Thread starter chop house
- Start date
Brians356
Gold $$ Contributor
Not to worry. Reading "physicist" was when I got interested. Thanks!
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. . . love the physics!
I was hoping there's be more focus on node and antinode and how that works regarding resonance and harmonics of that steel bar for a better understanding with tuning a cartridge to a barrel.
I was hoping there's be more focus on node and antinode and how that works regarding resonance and harmonics of that steel bar for a better understanding with tuning a cartridge to a barrel.
When I first starting reading about barrel harmonics, the impression I was getting seemed to focus on the "barrel whip" and the timing of the bullet leaving the muzzle at just the right point of that whip. High speed photography does show barrels whipping, but the bullet is long gone before the slightest amount visible whip can be seen. I got to thinking of the barrel more like a tuning fork along with the speed of sound through steel. Like a tuning fork, a harmonic is created upon the ignition of the powder and the harmonic wave traveling through the steel barrel starting from breach towards the muzzle. A barrel has a particular resonance and the harmonic wave vibration of the barrel where there's nodes and an antinodes. The trick is to align the timing the bullet exit with a harmonic node, not an antinode. One can change the timing of a bullet's exit from the muzzle to match a node, or . . . one can change the position of the node (the frequency) with a barrel tuner to match the node to the exit time of the bullets.
This is all quite an oversimplification as there are other things in play, like the effect of the bullet on the harmonics as it travels down the barrel, effects of a stock in contact with the barrel, etc.
Anyway, this my thinking about it these days.
butchlambert
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Back many years ago when I was visiting Ed Shilen about the Hewland trans in his Formula Ford race car we got on a different subject. His idea was to tune the barrel from a ringing sound to a thud. He brought out electronic headphones with a small mic on it. He told me to put them on and use the little microphone to listen to the barrel as he tapped it with a brass rod. I adjusted on the tuner until the ring turned to a thud.
Does it work? I don't know, but I own the headphones.
Does it work? I don't know, but I own the headphones.
butchlambert
Site $$ Sponsor
Varmint Al had a lot of studies of this subject. Even a pert on my tuner that I used to sell is there someplace.
Watch this video to really see barrel harmonics.
DirtySteve
Gold $$ Contributor
Butch, finding the dull spot is how black powder cartridge shooters get a way with shooting off cross sticks. Place the cross sticks on that mark. I mark mine with purple nail polish.
wkdickinson
Gold $$ Contributor
I found the video fascinating (intellectually), but not particularly informative as it relates to barrel harmonics. He discussed the "compression" of the steel and the resulting "bulge", but he didn't discuss the "wave form" (barrel whip), that we believe is created when a cartridge is fired. I readily admit I am a long way from being a physicist, but I'm not sure I really see how this relates to our pursuit of precision.
butchlambert
Site $$ Sponsor
Read a little of Varmint Al"s analysis.
I think your terminology is off. Your practical understanding may be correct but the wording of that statement is incorrect.
A wave node cant be at the muzzle end because it is unsupported. The muzzle will always be an antinode for the different standing harmonic vibration modes in a free floated rifle barrel supported on one end (the action).
A good analogy for the position of the muzzle of a rifle barrel is a pendulum. The muzzle is moving the fastest in the middle (neutral unflexed strait position) of its wave. This is point "D" in the diagram below. After the barrel crosses that center of the wave it begins to progressively slow down until it stops at its maximally flexed position and reverses direction. These max flexed positions are represented by points "G" and "A". It starts to speed up from point G or A achieving max velocity as it crosses the unflexed center point D starts the process again going to the other max flexed side. The blue graph shows velocity vs time for these positions and the red graph shows the position vs time. You can see at the bottom position (D) the velocity is at max in the blue graph and has the neutral position in he red graph. And you can see the sides (A&G) have zero velocity in the blue graph and peak positions on the red graph.
The two best positions are the max flexed positions. Close range bench rest guys will likely tune with shots falling as close to the peak as possible. BAB positions and FGF positions and exit timings as those spots have the least muzzle movement vs time hence the best raw accuracy.
Long range shooters need to use positive compensation to limit their vertical due to velocity spread so they likely tune on GFE or CBA positions and timings to insure their slower bullets are launched at a slightly higher angle to add some of the lost elevation at long range due to being slower.
Tuners do a few things. They do change the node points but that's a secondary concern really as some barrel movement is good for accuracy at extended ranges. The primary effects are these.
They lower the frequency of the vibrations making tuning windows larger.
They lower the amplitude of vibrations in the horizontal plane and give the barrel a more vertically oriented vibration pattern.
They allow you to change the vibration frequencies to change the point on the wave the bullet exits without having to adjust the seating depth of the bullet or powder charge. A simple dial on the end of the muzzle can make fine changes to where on the wave the bullet exits but does not change the bullets actual exit time to an appreciable degree.
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Well let me ask this.....Once the bulet has left the barrel, does
the next shot cancel out the previous shot's harmonics or is it
changing the timing for the follow up shot ?? Remember, the
first shot puts things in motion, and the second shot has to begin
with an already vibrating barrel. The above does not address this.
Again,,,,,thinking out loud
the next shot cancel out the previous shot's harmonics or is it
changing the timing for the follow up shot ?? Remember, the
first shot puts things in motion, and the second shot has to begin
with an already vibrating barrel. The above does not address this.
Again,,,,,thinking out loud
The vibrations don't last forever. They die out over time. The driving force (bullet with pressure behind) is gone in aprox 1.5 milliseconds. So it is excited from rest to max amplitude in about that time frame. Its likely that the amplitudes dampen themselves into irrelevancy in a timeframe much shorter than typical cycle times of bolt guns.
Basically back to nothing in .5 seconds.
jelenko
Gold $$ Contributor
The compression wave traverses the length of the barrel one way in ~ 0.2 milliseconds or ~ 0.4 milliseconds round trip. Each time it reflects from one end, some energy is lost, along with energy lost in propagation. By the time the next shot is going down the barrel, lets say one second later, there's been ~ 2500 full cycles from the last bullet.
jelenko
Gold $$ Contributor
The 'whip' in the barrel doesn't reach the muzzle before the bullet has left the barrel.
Chris Long developed a theory based on the same concept as this video.
Because accuracy nodes are found with differences in barrel time [the time a bullet is in the barrel] in the 10's of microseconds, he ruled out barrel whip because it's oscillations are too slow to account for accuracy node so close together in terms of the time the bullet is in the barrel.
wkdickinson
Gold $$ Contributor
I think many people would disagree with your first statement. If that is truly the case, why do "tuners" work?
Brians356
Gold $$ Contributor
Does a tuner increase the amplitude in the vertical plane?
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