Barrel harmonics in plain english

[rogina]

The tuners mass at the end of the barrel induces a larger droop in the barrel due to gravity and adds to the droop present from the barrels own weight. But the muzzle is an anti node putting that mass on the anti node dampens harmonics. Think about touching the open end of a tuning fork vs letting it ring free. The vibrations have to move more mass so unless they are given more energy to start with (more droop in the vertical plane) they will have less amplitude since they have to move more mass.

Since the tuner does nothing to add to the horizontal imbalance of a rifle barrel it does not induce stronger horizontal vibrations. Since the horizontal vibrations are the same strength with and without the tuner (close enough anyway) the extra mass of the tuner preferentially dampens those vibrations.

Tuners add to the vertical imbalance in the barrel and induce more energetic vertical vibrations. But those increased energy vibrations have to move more mass again so the net effect is near a wash in terms of amplitude (can be rifle dependent I think so ask a manufacturer for sure) but now you have eliminated some horizontal and gained more precise mechanical control over where on a vertical vibration wave your bullet leaves and lengthened your tuning window. These things are a significant benefit.

So, are you saying a tuner cannot effect the horizontal in a group?

 

[darkangel_r2]

So, are you saying a tuner cannot effect the horizontal in a group?

No it does. It makes it smaller. The horizontal vibrations don't become more energetic (significantly anyway) only the vertical do because of the added weight sagging the barrel more. So the horizontal vibrations are nearly the same energy as they were before but now they have to move more mass. This will do two things lower the frequency of the vibrations and reduce the amplitude of vibration in the horizontal plane.

 

[CNC-Dude]

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

I've also wondered how a vibrating barrel affects second, third and consecutive shots also. A few 6BR guys I've shot with shoot all 5 shots as fast as possible to get all the bullets out of the barrel before it heats up. They still shoot in the 1's and lower, and I would think the barrel is still vibrating with all shots except the first one. So I don't know if that turns out to be a pro or con....

 

[butchlambert]

I've also wondered how a vibrating barrel affects second, third and consecutive shots also. A few 6BR guys I've shot with shoot all 5 shots as fast as possible to get all the bullets out of the barrel before it heats up. They still shoot in the 1's and lower, and I would think the barrel is still vibrating with all shots except the first one. So I don't know if that turns out to be a pro or con....

The 1's and lower? WOW!!

 

[PRR1957]

Unless I missed someone bring up peak chamber pressure and its duration which would affect the amplitude of the harmonic for a particular gunpowder in a particular rifle barrel. Also. The firing pin would contribute somewhat as being the first source of vibration in a rifle.

 

[darkangel_r2]

I've also wondered how a vibrating barrel affects second, third and consecutive shots also. A few 6BR guys I've shot with shoot all 5 shots as fast as possible to get all the bullets out of the barrel before it heats up. They still shoot in the 1's and lower, and I would think the barrel is still vibrating with all shots except the first one. So I don't know if that turns out to be a pro or con....

My post replying to the one you quoted showed a test where vibrations returned to zero in about 1/2 a second.

 

[PRR1957]

Watch this video to really see barrel harmonics.

If you go to YouTube and search the title of the video posted by Pawnee Bill, the video playback speed can be slowed down more. If watched at 25% speed, you can see the muzzle flash is first, then the barrel starts to move.

 

[CNC-Dude]

The 1's and lower? WOW!!

Much better than I can do single feeding and taking my time compared to their rapid firing like they shoot!

 

[choprzrul]

Just kinda thinking out loud here....I've always 'visualized' barrel harmonics/whip in a 2D model. But now I am starting to wonder why I don't see bigger changes in POI during load ladder testing? A barrel swinging back and forth (up and down or left and right....what on earth would determine which way it swings???) would surely have pretty good POI changes?

If I ponder these barrel harmonics in 3D, as in a kind of 'bulge' travelling up and down the barrel from "longitudal" forces, it isn't 'whip' at all like was displayed for a pendulum swinging back and forth. Rather, it would look like an (exaggerated) golf ball going up and down a garden hose? If a 'bulge' is indeed causing the bore diameter to change as the wave travels up and down the barrel, the relationship of the bulge to when the bullet is released could change group sizes perhaps?

How does a barrel tuner screwed on the muzzle change all of this??

I dunno....just spitballing away here....

 

[choprzrul]

If you go to YouTube and search the title of the video posted by Pawnee Bill, the video playback speed can be slowed down more. If watched at 25% speed, you can see the muzzle flash is first, then the barrel starts to move.

Pay attention to the forearm. I swear I can see a ripple travelling down it just before the muzzle flash...

 

[darkangel_r2]

Just kinda thinking out loud here....I've always 'visualized' barrel harmonics/whip in a 2D model. But now I am starting to wonder why I don't see bigger changes in POI during load ladder testing? A barrel swinging back and forth (up and down or left and right....what on earth would determine which way it swings???) would surely have pretty good POI changes?

Depends on how close to bore axis your net recoil force is. If its very close the barrel gets disturbed much less.

If I ponder these barrel harmonics in 3D, as in a kind of 'bulge' travelling up and down the barrel from "longitudal" forces, it isn't 'whip' at all like was displayed for a pendulum swinging back and forth. Rather, it would look like an (exaggerated) golf ball going up and down a garden hose? If a 'bulge' is indeed causing the bore diameter to change as the wave travels up and down the barrel, the relationship of the bulge to when the bullet is released could change group sizes perhaps?

The issue with these theories is that a traveling bulge would only effect shot accuracy for a very small percentage of possible exit times. So if this were the main factor 95% of loads would be accurate and 5% inaccurate (arbitrary percentage chosen but you get the idea).

How does a barrel tuner screwed on the muzzle change all of this??

I dunno....just spitballing away here....

Check the links I posted earlier to vaughns rifle accuracy facts book. pg 84-87 details two worked examples of plotting group poi for different charge levels the graphs produced are enlightening.

 

[jelenko]

it isn't 'whip' at all like was displayed for a pendulum swinging back and forth. Rather, it would look like an (exaggerated) golf ball going up and down a garden hose?

That's a good way of describing what's shown in the video and Chris Long's model.

 

[Ledd Slinger]

Using barrel vibrations to tune a barrel

 

[butchlambert]

Much better than I can do single feeding and taking my time compared to their rapid firing like they shoot!

They must be using a different tape measure than we use.

 

[PRR1957]

Pay attention to the forearm. I swear I can see a ripple travelling down it just before the muzzle flash...

I saw some years ago on the cable show “Myth Busters” when they had one of their firearms experiments, and had a young woman who was on the factory Glock competition team. She had a long slide comp Glock. In one scene she was firing the pistol while video taped with one of the Phantom high speed, high def video cameras, and with each shot the dust/recoil spring extension cover on the front of the Tupperware frame was flapping with a gap about 1/4” wide. That example was one more reason for me to dislike the trend of plastic grip frame on handguns.

 

[CNC-Dude]

They must be using a different tape measure than we use.

This range uses the Shot Marker eTarget system.

 

[butchlambert]

This range uses the Shot Marker eTarget system.

Chuckle chuckle

 

[CNC-Dude]

That range held a V2 F-Open Class event last summer that had the top 64 big name guys in the sport there. I guess its good enough for them....

 

[Fuj]

Might do a test just for shits and giggles. I finished up chambering
a beater 7mm barrel just for fire forming brass. I propose to shoot
a group of ten, let the barrel cool then shoot ten more, but this
time, smack the barrel with my brass hammer prior to breaking
the shot. If the group is tighter, expect me to have a brass hammer
laying on my bench, the next match.

 

[PigButtons]

Might do a test just for shits and giggles. I finished up chambering
a beater 7mm barrel just for fire forming brass. I propose to shoot
a group of ten, let the barrel cool then shoot ten more, but this
time, smack the barrel with my brass hammer prior to breaking
the shot. If the group is tighter, expect me to have a brass hammer
laying on my bench, the next match.

And if you want tighter groups you can get a bigger hammer. I've seen a lot of posts saying that they have a hammer, wondering if it is a Lee, RCBS, ... Maybe someone will come out with a $600 hammer.