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What makes you think the dampening provided by the suppressor changes the frequency propagated by the ignition and pressure wave initiated at the chamber? . Isn't that what dampening is.... decreasing the frequency/amplitude of the vibration? How is the suppressor's weight different from any other "weight" you could attach to a barrel? Maybe a suppressor mostly just dampens the amplitude (strength) of the vibration. This seems to makes sense because the frequency of the vibration should really only change if the barrel material was changed. Then with a can you also get the benefit of the way it handles the pressure wave after the bullet exits the muzzle. I'm going to have to re-read Rifle Accuracy Facts now. It has a lot of big brain stuff on barrel vibration. Good thread everyone.
Last edited by dodgefan; 02/07/16.
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The people wringing their hands over Trump's rhetoric don't know what time it is in America.
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It is possible to damp the amplitude of a harmonic oscillation without changing its frequency. That was my proposition.
Jordan, I started a new job about 9-months ago that requires me to work on vibration problems. I am by no means an expert but have a very basic understanding of vibrations and mode shapes. Vibration analysis is a very specialized field within mechanical engineering that requires a lot of advanced training/coursework and practical experience... so I am just a hack In our lab, I have done a few "experimental modal tests". We do these tests to understand the natural frequencies and mode shapes of a structure when it gets excited at these frequencies. Remember the Tacoma Narrows bridge! We basically use a hammer with loadcell in the tip or a shaker to excite a structure. I've only done the hammer test. We suspend the structure with very soft isolators, excite the structure, and collect accelerometer data all over the structure. This data can then be used to create 3D models showing the mode shapes, like the bridge for example. These different natural frequencies and "modes" are properties of the structure, and it will behave in this way if the frequency is correct for that mode shape. In our tests, the rigid body mode is the lowest frequency where the whole thing moves in space, via the soft isolators. For a rifle barrel, the first vibration mode is generally believed to be a simple bend, with the muzzle projecting up and down... at a certain frequency. This first mode "shape" is basically the same for most barrels, but the frequency required to create this shape can be changed by altering the stiffness. We can alter the stiffness by chopping the barrel (stiffer) or adding mass at the muzzle (less stiff). Decreasing the stiffness makes the mode frequency lower. Some BR dudes talk about "slowing" a barrel down. What they are saying is that they want to lower the mode frequencies using the tuners. Their hypothesis is that the bullet exit needs to be during the upswing, and not during the downswing as Varmint Al illustrates at his website. I'm going out on a limb here, but I think everyone is still thinking about a barrel "whipping" wildly before the bullet exits the muzzle... or "oscillates". Per Varmint Al, this doesn't happen until AFTER the bullet leaves the barrel. The barrel is getting bent (deformed)... as shown in his animations, then the bullet exits. At Al's site, he listed ~135 Hz as the first mode frequency. This would be 1/135 = 0.007 seconds for one period. But if you assume that the barrel time is 0.001 seconds (also from Al's site), then the bullet exits well before we have one complete vibration period. The bullet exits at 14% of the periodic cycle. This could be during the upswing, but if the natural frequency and excitation creates a higher frequency vibration the barrel could be past the highest muzzle projection and on its way down. Hence, the BR dudes wanting to "slow" the barrel down. All that to say that I'm not sure that their goal is to reduce the amplitude, as the different modes can be pretty wild looking. Now the actual mode shape and frequency responsible for the muzzle projection, or excitation frequency, is a different story. Jason
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So.... a good ladder load could have less to do with barrel harmonics.... and more to do what happens as the bullet leaves, and immediately after the bullet leaves the bore?
Could there just be a jive between the bore exit pressure, bullet base, and crown shape that has less affect on the bullet than other loads of slightly higher and lower charges?
I wonder what would happen if you took a good ladder developed load, and then changed the crown shape drastically. That would do nothing to the harmonics of the barrel.... but could/would change the accuracy of the load.
If that did happen.... then it would be obvious that Ladder loads have less to do with internal harmonics, than they do with the relationship between pressure, bullet shape, and the crown. Which would also coincide with my theory as to why suppressors nearly always aid in accuracy.... while other "dampners" may not.
Just a thought.....
Dog, If you search for "traveling wave theory", Chris Long describes what he believes is a pressure ring that runs up and down the barrel. I think he claims that bullet exit while the ring is at the muzzle is bad juju. I'm not sure anyone has confirmed this or not, but remembered it after reading your post above. Jaosn
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4th Point, have you read Rifle Accuracy Facts by Vaughn? I don't have the education to understand a lot of what he talks about, but you seem to.
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No, but I'll check it out. Thanks!
Jason
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It's probably a good read for someone with an engineering background although dated. I don't have the education to get the most out of it.
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For you guys that shoot ladder tests, do you shoot several ladders and look for a trend? I would think that just shooting it once would introduce a the probability of human error influencing bullet impact points, especially at 600 yards.
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For you guys that shoot ladder tests, do you shoot several ladders and look for a trend? I would think that just shooting it once would introduce a the probability of human error influencing bullet impact points, especially at 600 yards. If you can't shoot, you can't shoot. Factory ammo is perfect for those who fit the bill
The people wringing their hands over Trump's rhetoric don't know what time it is in America.
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Gee I'm sorry, I thought I asked a legitimate question about the ladder test and repeatibility. Apparently not. Now if you guys will excuse me I'm going to go buy some more factory ammo while rcamuglia walks on water out to his 600 yard target.
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Gee I'm sorry, I thought I asked a legitimate question about the ladder test and repeatibility. Apparently not. Now if you guys will excuse me I'm going to go buy some more factory ammo while rcamuglia walks on water out to his 600 yard target. I know when I saw you here your factory loads were doing a serviceable job for you!!!!!!!
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Yep, that was those factory loaded 7mm STW 168 gr JLKs and that speed goat was only 456 yards. Not even far enough for a decent ladder test!
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Yep, that was those factory loaded 7mm STW 168 gr JLKs and that speed goat was only 456 yards. Not even far enough for a decent ladder test! Probably enuff gun for antelope, I believe..........
Last edited by wyoming260; 02/08/16.
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Now if you guys will excuse me I'm going to go buy some more factory ammo while rcamuglia walks on water out to his 600 yard target. I'm calling BS. Everyone knows you shouldn't shoot across water.
A wise man is frequently humbled.
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Gee I'm sorry, I thought I asked a legitimate question about the ladder test and repeatibility. Apparently not. Now if you guys will excuse me I'm going to go buy some more factory ammo while rcamuglia walks on water out to his 600 yard target. It's a good question but indicates your inexperience with long range shooting. If you can't hold on a 2" dot at 600 with a solid bench rest and squeeze the trigger without moving, then the long range Audette won't work for you. Stick to 100 yard development I usually drive to the target at 600. Another thing you'll learn with some more experience. LOL.
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Help me out here. In every description of the various versions of ladder and OCW load development methods I have seen, conventional wisdom says to ignore any horizontal distribution and attribute it to wind. We all know barrels oscillate upon firing but what law of physics makes them only oscillate in the vertical axis? Why don't they oscillate in the horizontal axis too? Or in a combination of vertical and horizontal axis? And, if that is the case, why are we ignoring the horizontal dispersion in ladder and OCW type load development?
Thanks,
John Now that we have 3 pages of shared knowledge, Lets start again: If you have a 20 shot ladder at .1 gr one shot steps and you find a 3 shot point (+/- .1) that is very good vertically but not horizontally what are you going to do about it? ...
Ray
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That's a good question, but only shows your inexperience with long-range shooting........
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[quote=Hondo64d]Help me out here. In every description of the various versions of ladder and OCW load development methods I have seen, conventional wisdom says to ignore any horizontal distribution and attribute it to wind. We all know barrels oscillate upon firing but what law of physics makes them only oscillate in the vertical axis? Why don't they oscillate in the horizontal axis too? Or in a combination of vertical and horizontal axis? And, if that is the case, why are we ignoring the horizontal dispersion in ladder and OCW type load development?
Thanks,
John .1 grain increments are too fine. Generally for .308 size cases .3 grains is good. For magnum cases .5 grains When you find consecutive shots that have nearly the same POI, you then shoot those individual loads to test. Pick the best and make seating depth adjustments if needed
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This was an entire 560 yard Audette. The impacts were all so close together that I didn't bother to mark them. I chose the highest velocity load under pressure
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