That's Interesting

[planeflyer21]

Interesting dittie on barrel flex.

 

[unforgiven]

I could see that movement being amplified with a lightweight or pencil barrel.

[sketch]

Good slow mo I knew of some movement but that is pretty noticeable. I'm also guessing his shoulder as anyone's gives more recoil/ flex movement but that was pretty good. Next time my buddy goes shooting w me ill do a slow mo vid of my 308 barrel and see what happens! No muzzle device.

[gnatshooter]

Good to see someone actually looking at at barrel harmonics instead of just talking about them. There certainly seems to be bad news there for compensators--vibrations like that easily cover 6 MOA or more.

 

It also appears there's room to doubt the popular wisdom of free floating the barrels. Let's hope the author continues doing good work like this.

[planeflyer21]

Good to see someone actually looking at at barrel harmonics instead of just talking about them. There certainly seems to be bad news there for compensators--vibrations like that easily cover 6 MOA or more.

 

It also appears there's room to doubt the popular wisdom of free floating the barrels. Let's hope the author continues doing good work like this.

 

Remember…free floating goes back to wood-and-steel days, when changes in humidity would apply unpredictable pressures against your rifle barrel changing the point of impact (POI).  Someone got the great idea to bed the action (for a solid, immobile base) and free float the barrel, to avoid such interference.

 

A second answer was to install bedding material in the whole stock, action seat and barrel channel, to prevent a warping stock from changing the contact points.

 

Another less expensive and time consuming option was making laminated wood stocks.

 

Then synthetics came along…but people are already entrenched in bedding actions with free floated barrels.  "My paw did it, and his paw did it, so I'm going to do it too!"

 

Going the other direction with barrel harmonics, the solution was to add rigidity.  The old dudes knew this.  Off the top of my head, the Winchester model 88 was designed to have the barrel contact the stock with a spot about 1" square, 12" back from the muzzle to effectively interrupt the start of the wave or "barrel whip".  Another way to "rigidize" the barrel is to add a type of double clamp, like the people that put Har-Bars on their Mini-14s…many claim to take their Mini from a 4 or 5 MOA gun down to 1 MOA or less with such an addition (cutting the spaghetti strand barrel back in length is another thing the Mini crowd does).  With the new Mini-14s, Ruger addressed the barrel whip by making a more rigid, thicker barrel, with a flange that butts up against the gas block that then tapers down to the older contour.

 

This barrel-whip has been addressed a variety of other ways too.  Tuneable muzzle devices, like the Browning BOSS, the QUE AMB, or the Ruger Mini-14 Target's "harmonic balancer" work great…if you use the same load every time and actually take the time to tune it in the first place.

 

There is a plethora of other gadgets designed to tune out barrel vibrations, ranging from a hunk of rubber than slides over the barrel to complicated barrel weighting systems.  Cool stuff.

 

On the video above, they mention that they also think that the excessive moving of the barrel may not be the barrel on an AR but flex in the aluminum action…something to consider.

[Dracomeister]

MANY years ago (more than I care to think about) at the tender age of 12 or so, I saved up my pennies and nickles and for a whoppin' $39.95 at the local Pawn Shop, bought my first "Deer Rifle".  It was a war surplus 7mm Mauser (can't remember what country it came from) and it had a spring loaded screw in the stock under the barrel.  At the time I didn't know what it was but then I learned that it was a "tunable damper" to help control barrel vibrations. 

 

Leap forward 40 years and the glass bedding job I did on my .270 Win. Remington 700.  I bedded the action and "free-floated" the barrel by rasping out the channel and the accuracy went to Hell in a hand basket. Oh Crap! What did I do? A gunsmith friend took the rifle (all the while describing my lack of parentage and discussing some rather unsavory personal habits), added a small mound of bedding at the very end of the stock (not more than 1/2" dia.) and wonder of wonders the 700 shot 1/2 MOA consistently. That was many years ago and the rifle still shoots to point of aim.  I'm a Mechanical Engineer and have a pretty good understanding of harmonics but that lesson stuck! Maybe I'm in the minority, but I'm not a fan of free floating barrels.  I think the old gun makers that put vibration dampers close to the muzzle were on to something!

[survivalshop]

All barrels will whip about when fired , with or with out a muzzle device. They whip up & down nicely . The only way to reduce a barrel's whipping is to increase the diameter. Like those bull barreled bench rest shooters.

I have no doubt that a muzzle device can add or subtract from this & the only way to eliminate this is ti have none on there .

 

The free float barrel debate has been going on for a long time & most believe it helps in keeping consistent accuracy . There are so many variables involved in what happens when you change this or that , as far as the way a rifled receiver fitment in a stock, its mind boggling .

There may be a combination of things needed to be done to properly free float any barreled action.

 

You can't compare a DI system to a piston system, two different harmonic & mechanical  patterns .

 

As far as what is flexing with in the AR platform , its mostly made of Aluminum , Made to be flexible, where the Steel Barrel is attached. 

Edited December 22, 2013 by survivalshop

[392heminut]

There certainly seems to be bad news there for compensators--vibrations like that easily cover 6 MOA or more.

 

 

I don't feel that a comp or brake really have any effect on accuracy as long as the bullet doesn't contact it on the way out. Muzzle devices work off of the gas propelling the bullet, and the gas doesn't even exit the barrel until after the bullet. In the video the barrel doesn't appear to move until the combustion gasses exit the barrel, at which time the bullet is already gone!

[planeflyer21]

I don't feel that a comp or brake really have any effect on accuracy as long as the bullet doesn't contact it on the way out. Muzzle devices work off of the gas propelling the bullet, and the gas doesn't even exit the barrel until after the bullet. In the video the barrel doesn't appear to move until the combustion gasses exit the barrel, at which time the bullet is already gone!

 

There was an article a couple of decades ago (wow…I can say that now) on muzzle brakes, which went to the nth degree on breaking down how they work.

 

What took them a long time to explain in the article, was how the comp/brake was working before the bullet exited, utilizing the air in the barrel.  When fired, the bullet compresses all the ambient air in the barrel in front of it, and this compressed air is what first exits the muzzle, hence the brake/comp.

 

It was very in depth but yes you are right, by the time the harmonics really kick in the bullet is on its way.

[unforgiven]

Good info guys. <thumbsup>

[392heminut]

What took them a long time to explain in the article, was how the comp/brake was working before the bullet exited, utilizing the air in the barrel.  When fired, the bullet compresses all the ambient air in the barrel in front of it, and this compressed air is what first exits the muzzle, hence the brake/comp.

 

 

Damn Jon, I hadn't even considered that. But then again, I ain't the sharpest pencil in the box either! ;D

[planeflyer21]

What?!

 

They gave you something other than crayons?!?

[Dane Armory]

A guy I met at the range once (The Rifleman) , explained about barrel harmonics and the use of rubber rings on the end which dampened the effect for a quicker follow up shot. The Olympic shooters use them.

[gnatshooter]

The more I look at that video, the more I think, "No way is a barrel that flexible." Maybe there's something about the camera pixelating the image or something.

[planeflyer21]

Many speeds, many guns, many angles, many different cameras.

 

 

 

 

 

Notice the difference between that first, current production Mini-14 and the second, old production Mini-14 spaghetti barrel.

 

This next one is an air rifle…pretty flexy, as it doesn't need to contain the pressures a firearm does.

 

 

This one is good, as there is straigh stuff in the background.

 

 

AK:  

 

And this last dude puts straight lines on some of the film clips for reference, last rifle is labelled as an "AR-10 .308"

 

 

Somewhere (can't find it now) there used to be military or ammo/firearms company footage, of rifles mounted rigidly on a fixed surface, fired and then filmed in slow motion against a background of a grid (1" squares I beleive).  The barrel flex was astounding.

[98Z5V]

All materials being the same (metal grade, heat treating, diameter, taper of diameter, etc), shorter barrels will whip less. 

 

That's the whole premise of going shorter on accuracy guns, and the whole thread that we started about it.  There's some great info in that thread that directly ties into this conversation, right here. 

[seasprite]

Another thing to consider is the load. I mean if you can get the bullet to exit at the same point during the whip your going to have an more accurate rifle then one that exit at a different point in time. Isn't this why we identify the scatter nodes along with the accuracy nodes when we work up a load is to find what works best with our barrel harmonics. At least this is what I've been basing my load development on. 

[jtallen83]

Another thing to consider is the load. I mean if you can get the bullet to exit at the same point during the whip your going to have an more accurate rifle then one that exit at a different point in time. Isn't this why we identify the scatter nodes along with the accuracy nodes when we work up a load is to find what works best with our barrel harmonics. At least this is what I've been basing my load development on. 

I use the ladder test when working up rifle loads for this reason, make the smallest change on the rifle like a new flash hider or comp and the old data is out the window. You want the bullet to be exiting on the top or bottom of the wave where the dwell is the longest, this gives you the most tolerance in load consistency.

[Dracomeister]

Got out on the range today to work up a new load.  Two rifles, LR-308 with 16" standard barrel and compensator, and a custom Mauser 24" light sporter also in .308.  Identical loads using 168 gn Hornady BTHP Match over H-4895 ranging from 37.5 gn to 43.0 gn.  The target on the left is the Mauser, the right is the LR 308.  You can't see all of the rounds from the Mauser because the last three strung to 3" above the target.  Obviously some of the variance was the load but I believe the stiffness of the 16" barrel was a big factor.

[Tripledeuce]

    BBL movement is NOT only up and down.

   If you could film in 3D, you'd find the bbl is actually moving in a sprial, as the bullet moves through the rifiling.

  As we have noticesd, "sweet spots" or :nodes" vary in different bbls.

  I'v tested free floting bbls, bedded, with no pressure bbls, bedded with upward pressure bbls, and floating with pressure bbls.

   There MUST be a reason that the benchrest crowd, for the great part, use floating bbls.

   I'v only been working with AR's for a short time, but have already taken several guns that would only shoot 2-4" groups, and by adding only a FF handguard, reduced the group size tremendously.

    I have yet to have it work in the reverse!

    Also, rember!   we have a gas block, almost at the center of the bbl, that in, and of itself forms  a "dampener".

   Another experment I plan to try, later this summer, is to machine several "dampeners" steel, aluminum, rubber, etc, and start with them at the muzzle, and move them back an inch at a time and see what happens,

    Respectfully

    Terry

[jrtmasp]

<thumbsup> Great job guys. A ton of interesting information.