THE TRUTH ABOUT BARREL MOVEMENT ???

[Zero333]

Here we go... found a few examples in slow-motion...

 

[BoydAllen]

Seems like the barrel would move in all directions.

If you spend a little time reading Vaughn's "Rifle Accuracy Facts" you will come to know that during recoil a rifle tends to rotate around its center of mass, which generally is below the CL of the bore. This rotation has the muzzle of a floated barrel lagging the rotation of the rifle very slightly which loads the barrel vertically, at some point the barrel reaches a limit and starts back the other way, relative to the rifle. There is no equivalent situation for horizontal movement.

 

[Tesoro]

Because of barrel whip sometimes a higher charge weight the lower the point of impact. Speaks for itself.

Here is pic for example....

View attachment 1543460

So, if you had a tuner on this barrel then the load you would want to chose to tweak using the tuner would be when the barrel is close to the end of its rise? ie one in the first 4?

 

[Zero333]

So, if you had a tuner on this barrel then the load you would want to chose to tweak using the tuner would be when the barrel is close to the end of its rise? ie one in the first 4?

Yes, it only makes sense that the widest nodes will be when the muzzle reaches the top or the bottom of it's "whip".

 

[gunsandgunsmithing]

So, if you had a tuner on this barrel then the load you would want to chose to tweak using the tuner would be when the barrel is close to the end of its rise? ie one in the first 4?

Yes, but you're not seeing those small movements in the videos, much if at all before bullet exit. Most of what I see in these is the big movement after the bullet leaves that are at a much higher amplitude..but, vibration starts essentially when the fp falls

 

[J.D.Erwin]

Also, most people think the barrel whip is up and down, while the target certainly shows there is left to right harmonics at play as well.

The barrel is a circle ! so is the harmonies its moving IMO 360 degree

 

[gunsandgunsmithing]

The barrel is a circle ! so is the harmonies its moving IMO 360 degree

Not as much as you might think but yes, there is a lateral motion as well. I'd assume this is at least in part from the twist of the rifling but there may be more than a single cause. Just never tested that aspect far but you can see the lateral in group shape and poi of the groups. I've never found a tuner to ONLY control vertical. I've heard that said but have never seen it nor could I explain it if it were the case. But, the movement is vertically biased, if for no other reason than, gravity. I've tested and measured bbl movement but not the actual forces as to why they move the way they do. That can probably be explained by the right person. It's just me in this aspect. I'd suspect cg is a factor as well but twist has to play a part...just not as big as the vertical aspect. Another thing to consider, I think along your lines...is the bore is never perfectly centered in that "circle."

 

[Bill Norris]

The barrel is a circle ! so is the harmonies its moving IMO 360 degree

Yea, it seems there would have to be a certain amount of horizontal movement.

 

[Tesoro]

The barrel is a circle ! so is the harmonies its moving IMO 360 degree

Read BoydAllen post above

 

[gunsandgunsmithing]

Read BoydAllen post above

Yes but...in which plane does it rotate? I think you might be seeing it as only around the cl of the bore rather than longitudinally as well. As in...in simple terms, the balance point of the rifle, fore and aft, in the rest. There's some vertical! Lol!

 

[Alex Wheeler]

The harmonics in the barrel that effect poi are so small they are masked by the movement of the whole barrel. If the barrel was mounted rock solid and didnt recoil you could see more of the barrel harmonics. But they would probably be far more violent if you mounted it that way. This is why I always tell guys muzzle brakes dont tame down heavy recoiling rifles. They reduce felt recoil, but all that movement the bullet sees happens before the muzzle brake can do anything. You can tame down a magnum with a brake and make it feel good but it will never shoot as well as the heavier rifle. Even if the heavy one has no brake and kicks you twice as hard.

 

[Alex Wheeler]

If you spend a little time reading Vaughn's "Rifle Accuracy Facts" you will come to know that during recoil a rifle tends to rotate around its center of mass, which generally is below the CL of the bore. This rotation has the muzzle of a floated barrel lagging the rotation of the rifle very slightly which loads the barrel vertically, at some point the barrel reaches a limit and starts back the other way, relative to the rifle. There is no equivalent situation for horizontal movement.

This would apply to the way the rest of the rifle imparts movement to the barrel. But in the barrel itself there is certainly a horizontal component. The fact that most rifles have a c/g lower than the bore, and gravity has the barrel preloaded is likely why we see more vertical the horizontal. In some rifles like s/r br rifles the c/g is much closer to the bore c/l. That coupled with short stiff barrels probably explains why they dont shoot anywhere near the vertical that most other types of rifles can when out of tune. I suspect if we built a rifle with the c/g in line with the bore c/l and fired it in a zero gravity environment, we would see the same horizontal as vertical when working with the tune. May not even be able to tune it actually since we have removed that main vertical harmonic?

 

[gunsandgunsmithing]

The harmonics in the barrel that effect poi are so small they are masked by the movement of the whole barrel. If the barrel was mounted rock solid and didnt recoil you could see more of the barrel harmonics. But they would probably be far more violent if you mounted it that way. This is why I always tell guys muzzle brakes dont take down heavy recoiling rifles. They reduce felt recoil, but all that movement the bullet sees happens before the muzzle brake can do anything. You can tame down a magnum with a brake and make it feel good but it will never shoot as well as the heavier rifle. Even if the heavy one has no brake and kicks you twice as hard.

I've seen tune change by shooting significantly uphill. Not talking LR POI here but tune. So yes, I agree with ya.

 

[gunsandgunsmithing]

This would apply to the way the rest of the rifle imparts movement to the barrel. But in the barrel itself there is certainly a horizontal component. The fact that most rifles have a c/g lower than the bore, and gravity has the barrel preloaded is likely why we see more vertical the horizontal. In some rifles like s/r br rifles the c/g is much closer to the bore c/l. That coupled with short stiff barrels probably explains why they dont shoot anywhere near the vertical that most other types of rifles can when out of tune. I suspect if we built a rifle with the c/g in line with the bore c/l and fired it in a zero gravity environment, we would see the same horizontal as vertical when working with the tune. May not even be able to tune it actually since we have removed that main vertical harmonic?

Maybe, but there's also the forced deformation under pressure as the bullet traverses the bbl..a solid moving section of bbl. I would think those forces would still be at play but maybe equal in all directions, in a vacuum. IDK.

 

[Tesoro]

The harmonics in the barrel that effect poi are so small they are masked by the movement of the whole barrel. If the barrel was mounted rock solid and didnt recoil you could see more of the barrel harmonics. But they would probably be far more violent if you mounted it that way. This is why I always tell guys muzzle brakes dont tame down heavy recoiling rifles. They reduce felt recoil, but all that movement the bullet sees happens before the muzzle brake can do anything. You can tame down a magnum with a brake and make it feel good but it will never shoot as well as the heavier rifle. Even if the heavy one has no brake and kicks you twice as hard.

curious..when you build your (very nice) rifles, do you time/clock the barrels to 12 o'clock? I assume even the best of the best barrels are going to have a little banana in them.

 

[CharlieNC]

When I shoot a ladder I measure deviation in horizontal as well as vertical poi, and most of the time they are highly correlated. Meaning the barrel vibration is in both directions, which is fortunate when tuning.

 

[gunsandgunsmithing]

curious..when you build your (very nice) rifles, do you time/clock the barrels to 12 o'clock? I assume even the best of the best barrels are going to have a little banana in them.

The way I look at that is, the banana doesn't move. It's a constant and I've not seen it matter to tune, clocked or not..fwiw.

 

[Alex Wheeler]

curious..when you build your (very nice) rifles, do you time/clock the barrels to 12 o'clock? I assume even the best of the best barrels are going to have a little banana in them.

Its not a banana, it wanders in any way it wants to. Sometimes only part of the bore, sometimes all the way down. Fortunately how much or how little seems to have zero effect on accuracy, at least in my experience with the way I chamber. To answer your question, yes I clock every barrel.

 

[BoydAllen]

The harmonics in the barrel that effect poi are so small they are masked by the movement of the whole barrel. If the barrel was mounted rock solid and didnt recoil you could see more of the barrel harmonics. But they would probably be far more violent if you mounted it that way. This is why I always tell guys muzzle brakes dont tame down heavy recoiling rifles. They reduce felt recoil, but all that movement the bullet sees happens before the muzzle brake can do anything. You can tame down a magnum with a brake and make it feel good but it will never shoot as well as the heavier rifle. Even if the heavy one has no brake and kicks you twice as hard.

I did not mean to say that there was no horizontal movement, but just explain what generates a lot of the vertical movement. There is a lot more going on than I wrote about. You may also have a copy, but in case you do not, Vaughn's book is available for free on line. He did a lot of work with an accelerometer mounted on barrels' muzzles and an oscilloscope. For one experiment he measured the amplitude and frequency of muzzle vibration of a barrel that was part of a rail gun and then mounted weights high on the sliding part that the barreled action was part of, to bring the center of mass of that assembly to the barrel's centerline. this had a major effect on the amplitude of the muzzles vibration, reducing it significantly. On the tunability of a balanced rifle (center on mass on bore CL0) a friend has such a rifle, a short range group heavy varmint (13.5# max. wt.) and he has had no trouble tuning it to very fine accuracy, with a very broad node and less apparent temperature sensitivity.

 

[jds holler]

Would be interesting see if two barrels of similar dimensions, but one being octagon, differ in the whip factor. jd