Extreme Accuracy Using a Muzzle Device/'Tuner'

[GREEN607]

Posting this for those here who are thinking about trying a MD (also known as 'tuners') to improve accuracy of POI on rifles.

This post (linked) and the included 5 min. movie are the work of world-renowned custom rimfire gun builder, Bill Calfee, of Borden, Indiana.

The sole purpose of a muzzle device, is to move the 'dead spot' in the barrel's oscillation upon firing.... to the crown of the muzzle. Bill has made a third movie and will post a fourth, soon. I just wanted to help you understand the barrel's vibration (from ignition) and how to eliminate it's affect on the bullet... thus improving accuracy in your rifle.

Here's the link to Bill's post over at World Wide Accuracy forum, for "barrel ringing movie #2. To see what the theory of MD's is, just click on the still pic below where it says 'The Movie' in his post. Enjoy!

Barrel ringing movie #2

 

[jjlaughner]

pretty cool

 

[MegaTank]

Have you seen the Browning BOSS system?

 

[aclark]

I think esrice or lovemywoods did a full write up on a barrel tuning system for rim fire .22.

 

[GREEN607]

Movie #4... Stopping the barrel muzzle w/ a steel MD (Calfee)


Click on the link. Movie is at bottom of his post. (Click on still photo)

http://wwaccuracy.com/showthread.php?4115-Barrel-ringing-movie-4

 

[padawan]

Very interesting.

 

[Hohn]

The Browning BOSS came out a long time ago. And the effect of barrel vibration has been known for a long time.

I'm missing something, apparently.

 

[mammynun]

At 4:00 in the video at the first link (Barrel ringing movie #2), he states that he's doing the "ring testing" without the barrel being mounted in the action/receiver. I'm not a gunsmith, but it seems to me that when the barrel is mounted that the [STRIKE]effective[/STRIKE] acoustically resonant length would be shorter, making the pitch higher. If the pitch is higher, wouldn't the resonant point (parallel node) move?

As far as "some electronic guru" coming up with a way to measure, three or four of these and a Mackie 1202 mixer would work. Fishman | SBT-HP Soundboard Transducer for Harp & Piano

 

[GREEN607]

The Browning BOSS came out a long time ago. And the effect of barrel vibration has been known for a long time.

I'm missing something, apparently.

Bill Calfee introduced his rimfire muzzle device, in the late 1980's. He is just sharing the science and knowledge behind it, NOW on his forum. -Lee

 

[padawan]

Bill Calfee introduced his rimfire muzzle device, in the late 1980's. He is just sharing the science and knowledge behind it, NOW on his forum. -Lee

That was my thought too... He was sharing his knowledge on a series of videos.

 

[Hohn]

At 4:00 in the video at the first link (Barrel ringing movie #2), he states that he's doing the "ring testing" without the barrel being mounted in the action/receiver. I'm not a gunsmith, but it seems to me that when the barrel is mounted that the [STRIKE]effective[/STRIKE] acoustically resonant length would be shorter, making the pitch higher. If the pitch is higher, wouldn't the resonant point (parallel node) move?

As far as "some electronic guru" coming up with a way to measure, three or four of these and a Mackie 1202 mixer would work. Fishman | SBT-HP Soundboard Transducer for Harp & Piano

Installing the barrel in the action will not change the effective modal frequency of the barrel, because it affects neither stiffness nor mass. (freq proportional to stiffness ^2/mass)

However, a stock that isn't free floated might. If you have a mannlicher-style stock, it adds to the effective stiffness of the barrel (in only one plane). The resulting resonance is likely multimodal, and has two primary frequencies, one in the plane of max stiffness, the other in plane of least stiffness.

A barrel of uniform, untapered profile is pretty easy to understand, because the stiffness is the same everywhere relative to the bore axis. This might actually be a bad thing.



This is already too long, but I'll indulge a little MSME theory here:

All of the energy of the cartridge combustion has to go somewhere. It ends up stimulating vibration in the barrel. This is call "forcing function". However, the barrel's resonance is largely independent of forcing function. If I hit it with a brass mallet instead of a plastic or rubber mallet, it will sound different at first-- but the resulting resonance will be exactly the same after the initial hit. Resonance is what's left undamped. Initially, EVERYTHING is stimulated, but there is lots of damping that quickly suppresses the initial response, leaving only the undamped (resonances) behind. This is why my choice of guitar pick only affects the attack of the string, not the tone of a held note.

The barrel will want to move a certain way in response. This movement has both directional elements (which directions the barrel moves) as well as time elements (frequency) and magnitude (amplitude). Frequency, direction, amplitude-- those are the three essential variables of resonant motion.

Now, what do we want from a barrel? Do we want minimum amplitude so that bullet scatter is minimized? Or do we want want maximum dispersion for the lowest AVERAGE displacement?

You can see where we are headed: you can either make a barrel very consistent (and very insensitive to ammo variation) or you can hyper-tune it for lowest amplitude and make something that is VERY sensitive to ammo variation.

Modal resonances in a barrel on on the order of a couple hundred hertz. Lets say 300Hz. A maximum displacement might be a half a millimeter at that frequency. Speed of sound through steel is 6100 meters per second, and at 300hz that means you end up with a wavelength of about 20 meters.

It's a good thing to have the wavelength longer than the barrel length, because the wave will reflect at the end of the barrel. If the wavelength is exactly twice (or an even multiple of the barrel length), then the reflected wave will almost totally cancel out the initial wave and the barrel will settle down quickly.


Not that it matters a ton. At 3000fps, it only takes 2 milliseconds to travel down a 24" barrel (obviously, this is an overestimate as the bullet doesn't instantly achieve 3000fps). in 2 milliseconds, your 20 meter long wave travelling at 6100 meters per second has only managed to get a little over halfway down the barrel. (12."meters of wave" have moved down the barrel)


Stiffer barrels are more accurate barrels not just because they move the vibration to a higher frequency. It's also the fact that the higher frequency has less amplitude-- the total barrel movement is less. Remember, the energy from the cartridge hasn't changed, so the higher frequency MUST produce lower amplitude.


Thus, the fluted barrel-- increased stiffness without increasing the weight as much. Always remember that stiffness is SQUARED and weight is not. So even if your 20% increase in stiffness comes with 20% more weight, it's still a much better barrel for accuracy.

Ideally, you'd want a super heavy profiled barrel with very deep flutes to give you most of the stiffness gain with the least amount of added weight.

The extra cooling area is just bonus.

 

[padawan]

Very nice write-up Hohn. I may print it out.