I understand what people -say- about barrel harmonics and why everyone attempts to free float their barrel. But I want to see it. I expect to see the barrel develop some sort of wave as the bullet travels down the bore. I have been looking for a slow motion video that would show a barrel's movement during the shot but I can't find one. Is anyone aware of a video that shows this process in clear detail?
Slo-mo barrel harmonics video
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gohring3006
Well-Known Member
Check out JE Customs videos in the "videos of tech stuff and reviews" sub forum.
It's the Recoil reduction of the 300 Rum thread on page two. It shows what happens during the shot. The video on page three of the thread posted in his reply to me. It shows a pretty good video of barrel flex..
(For some reason my phone won't let me post links sorry..)
It's the Recoil reduction of the 300 Rum thread on page two. It shows what happens during the shot. The video on page three of the thread posted in his reply to me. It shows a pretty good video of barrel flex..
(For some reason my phone won't let me post links sorry..)
Thanks, I just watched that video. He was filming what I would like to see, but his equipment doesn't really capture what I'm looking for. With the frames per second he was able to capture, you can only see major bends in the rifle barrel depending on whether he used a brake and what kind. It does not show enough detail to really see a harmonic wave roll through the barrel; that's what I'm hoping to see. With the significant bends in the rifle he was seeing with unbraked shots, I'm sure those barrels were hitting the stock. With that in mind, I wonder if most free floated barrels are hitting the stock anyway. Then again, it is my understanding that those rifles being locked up in the lead sled perform much differently than one that is held to the shoulder.
gohring3006
Well-Known Member
I make sure I have at least .020 of clearance between the stock and barrel. I did a test with a sporter barrel rifle. I used whiteout and marked the barrel and shot it and checks for impact. There was impact with the factory barrel channel cut out...
J E Custom
Well-Known Member
Maybe I can help explain this phenomenon.
Years ago I saw a film of barrel testing from Aberdeen Proving grounds that the military doing and have been trying to find it to post also.
They had gone to a lot of trouble to try and figure out what was causing problems in some barrels.
The first thing I noticed in small contoured barrels, was the torqueing. the test barrel would twist the opposite direction as the rifling twist from bullet torque. Heavy barrels did this much less.
The next phenomenon was whipping in all directions. (I imagine that's where the term Buggy whip barrel came from) Again the heaver barrels were not as prone to this as much as the light ones.
Also, the longer the barrel is, the more this effect is present. I was unable to see any wave effect
but felt it was probably there but to difficult to see with everything else going on.
In the test video, we knew there were problems due to the contact markings on the inside and sides of the stocks with any amount of clearance (We had rifles with .060 clearance between the barrel and stock) and needed a way to show this effect. restraining the stock was the only way to show how much force was being applied and measuring/Videoing it. In some cases, the stock help to minimize the amount of flexing.
The problem/force is still there even if you hold the rifle offhand, you just cant measure it. If you notice in the video we moved the restraint to different locations and got the same results.
All barrels flex, whip, and torque to some degree depending on barrel size. In Testing for the accuracy node you are looking for that point that the barrel reacts the exact same every time
to improve accuracy.(The harmonics are very dependable/consistent).
Bull barrels or heavy contours are the best way to minimize these effects, but most don't want to carry a 12 pound rifle so finding the NODE is the normal method for controlling, Not eliminating this phenomena.
To see some of the other effects, a camera with 1500+ frames a second would be required. (We
used 240 frames a second). Barrels without brakes still have these effects and must be loaded to minimize these effects. Normally the force is directed along the centerline of the bore and bending
is not as prevalent. With top ported or uneven ports, there is an uneven force that compounds the
problem.
So the point is, to minimize this problem by design, and load to make it consistent.
Hope this helps
J E CUSTOM
Jay Kyle
Well-Known Member
This would be a great study for a university physics or eng/phys dept looking for a project - since they'll have the equipment needed to capture the event.
I've been trying to find some more information about this. Is there some place that you can point me to? Specifically, I'm interested in how load development reduces the effects of whipping and if it is optimal to have the bullet leave the barrel at the extreme point of the whip or at the point where the barrel is under the least amount of stress.
So a shorter, heavy barrel is less impacted by harmonic forces. And folks use those types of barrels for accurate shooting.
That seems to say that harmonic forces on the barrel are a bad thing. And if it is bad it seems to be something you would want to control/reduce (shorter/heavier barrel) instead of accommodating (long/thin/free floating barrels that are allowed to whip).
To take this logic to the extreme, if you had a truck size hunk of steel with a bore drilled through it and fired a shot. There would be no harmonics at play. Would we see a superior result due to the lack of harmonics? Or is there any benefit from the harmonic process?
If not, it seems like the wrong approach to free float a barrel. Seems like you would want to lock it in and reduce movement wherever possible. Of course, weight is an issue, and most people want a lightweight barrel and perhaps this is the only reasonable approach for a shoulder fired rifle.
I guess what I'm thinking/realizing is that a free floating barrel may not be a performance enhancing feature but rather a compromise. Are we only free floating because we realize "oh crap, that thin barrel is going to bend/whip when I shoot it and if it hits the stock that's going to mess up my shot"?
That seems to say that harmonic forces on the barrel are a bad thing. And if it is bad it seems to be something you would want to control/reduce (shorter/heavier barrel) instead of accommodating (long/thin/free floating barrels that are allowed to whip).
To take this logic to the extreme, if you had a truck size hunk of steel with a bore drilled through it and fired a shot. There would be no harmonics at play. Would we see a superior result due to the lack of harmonics? Or is there any benefit from the harmonic process?
If not, it seems like the wrong approach to free float a barrel. Seems like you would want to lock it in and reduce movement wherever possible. Of course, weight is an issue, and most people want a lightweight barrel and perhaps this is the only reasonable approach for a shoulder fired rifle.
I guess what I'm thinking/realizing is that a free floating barrel may not be a performance enhancing feature but rather a compromise. Are we only free floating because we realize "oh crap, that thin barrel is going to bend/whip when I shoot it and if it hits the stock that's going to mess up my shot"?
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gohring3006
Well-Known Member
The Harmonics are unavoidable.
The heavier barrel make the standing wave less severe.
The thinner barrel has a large wave.
The less whip the wider the node.
There is a good demonstration of this on TiborsaurusRex's video series Sniper 101, titled.
"Rifle Vibrations and Harmonics Explained"...
The heavier barrel make the standing wave less severe.
The thinner barrel has a large wave.
The less whip the wider the node.
There is a good demonstration of this on TiborsaurusRex's video series Sniper 101, titled.
"Rifle Vibrations and Harmonics Explained"...
J E Custom
Well-Known Member
All good questions
Q1=Yes. A shorter heavier barrel is normally used in bench rest shooting where velocity is not that important and accuracy means everything.
Q2= harmonics are a bad thing and we take great steps to minimize the effects of them buy bedding and using the heaviest/shortest barrel that is practical.
Q3= A truck sized barrel/chunk is not practical and there would still be harmonics but they would be reduced by the mass and have little if any effect on the accuracy. long, thin barrels are very susceptible to harmonics hence the reason that most factory rifles with these barrels have tip pressure applied by the stock. This can be very effective for one shot consistency by effectively
shortening the free barrel length. The problem with dealing with it this way is they only want one or two loads and any heating of the barrel changes the POI.
Q4=Free floating a barrel can do several things. It can improve the consistency of the barrel harmonics by eliminating any outside influences allowing the barrel to do the same thing every time improving the consistency shot to shot. The down side is that sometimes it allows the barrel to move to freely hurting accuracy/consistency. Some bed a small portion of the barrel shank in an effort to effectively shorten the barrel length and reduce the harmonics. this helps sometimes and may hurt other times.
When we tune the harmonics, what we are doing is trying to control them where the bullet leaves the barrel muzzle at the exact same position every time. There are lots of other steps to control/minimize harmonics. and in order to have a weapon that is manageable in the field we have to manage harmonics. It is important to understand harmonics and how to deal with them if accuracy is important.
I have said this many times and even been quoted by some. "The only advantage a light rifle has over a heavy rifle Is weight, all other advantages go to the heavier rifle".
J E CUSTOM
Can stock material minimize barrel harmonics? For example, a steel stock compared to a laminated wood stock. If a stock is very rigid, wouldn't some of that energy be relieved through the barrel? Would laminated wood adsorb some of that energy, making a practical difference in barrel harmonics?
Mikecr
Well-Known Member
There is another vibration, which is the basis of OBT. That is a pressure induced wave traveling back & forth, source to muzzle & back. A wave of bore dimension change.
And then there are vibrational waves from pretty much any rigid to the barrel interface/pressure point. This, including chambered tensions setup by crooked ammo, or your thumb resting on the action tang. You can read about these in 'Rifle Accuracy Facts'.
These could not be seen with video directly as they are dimensionally tiny. But they can be measured with strain gages or laser mic and a DAS. That is, if you could stop pretty much all other movements, and employed a very high sample rate (the waves travel at the speed of sound in steel). Either that or measure all movements at once..
Truly seeing what's happening how much & when is not an easy endeavor.
And then there are vibrational waves from pretty much any rigid to the barrel interface/pressure point. This, including chambered tensions setup by crooked ammo, or your thumb resting on the action tang. You can read about these in 'Rifle Accuracy Facts'.
These could not be seen with video directly as they are dimensionally tiny. But they can be measured with strain gages or laser mic and a DAS. That is, if you could stop pretty much all other movements, and employed a very high sample rate (the waves travel at the speed of sound in steel). Either that or measure all movements at once..
Truly seeing what's happening how much & when is not an easy endeavor.
J E Custom
Well-Known Member
In fact yes.
I believe that laminate does just that, because the grain runs in many directions causing the shock wave to be dispersed in many directions. There are many discussions on different stock materials if you do a search.
I for one changed all of my rifles that had composite stocks to laminate stocks and accuracy was improved across the board. Some improvements were small 5 to 10% improvements and some were as much as 50%.
I found that while shooting the composites, there would be a ringing or Twanging sound come from the but stock when fired. the laminates are very sound dead and I think they help dampen
harmonics.
Here is a post on this subject that may be of interest.
http://www.longrangehunting.com/forums/f94/recoil-values-different-stocks-168848/
J E CUSTOM
