Sine waves

[gsardokla]

I would think it's a big ass explosion in the chamber that causes sine waves.

While there is some vibration introduced by the powder deflagration (NOT explosion), the significant vibrations are due to projectile friction both torsionally and longitudinally. That projectile is trying to twist and pull the barrel along with itself. It's really impressive to see a super-slow motion of 155mm gun tubes when firing standard HE rounds. It's over so quickly, you just don't see it, literally, in the blink of an eye. Although much smaller, small arms projectiles do the same thing. Interior ballistics is interesting.

 

[AlNyhus]

The powder wave on necks is a good reference as to neck clearance. -Al

 

[jdh47]

Dark magic.

 

[ebb]

Much ado about nothing

 

[powderbrake]

How do you know the frequency of the sine wave, which determines the 'zero', is the same when fired vs when hit with a mallet?

Because the barrel is vibrating at its "natural frequency", which is set by it's shape and mounting.

 

[rijndael]

Because the barrel is vibrating at its "natural frequency", which is set by it's shape and mounting.

Post #3 says it's also based on the bullet going down the barrel.

 

[rijndael]

An interesting read on the sine wave in barrels:

RSI - General Reloading Tips

Barrel Harmonics, Timing & Theory

www.shootingsoftware.com

 

[Intheshop]

Cast bullets;

Neck clearance can be changed with bullet diameter... independent of,case neck thickness.

IOW's;we can run the same load pressure,same annealed state,same jam,alloy,etc...and by changing neck clearance with bullet diameter,see the wave come and go.

WRT jacketed; gut reaction is, set your clearance carefully. Too many "little things" to make a blanket statement that there must be "X" clearance.

 

[1911nut]

Sine wave soot marks on the case neck

Well we settled that.

It’s powder charge
It’s neck clearance
It’s the lugs on the bolt
It’s the amount of primer crush
It’s slow powder=slow burn

It’s probably not dark magic

 

[jackieschmidt]

Jackie what are you running for neck clearance from brass to chamber? That is a beautiful pattern on the neck. Textbook. Looks just like the drawing in Tony Boyer’s book. Is that from a single firing? I imagine so, because you could never get the brass to index you the same position multiple times.
Dave

I run .0015 on my 6PPC and BR, .0025 on my 30BR.

 

[Steve Blair]

 

[Dusty Stevens]

View attachment 1345911

Thats a “wave sign” not a sign wave!

 

[timeout]

While there is some vibration introduced by the powder deflagration (NOT explosion), the significant vibrations are due to projectile friction both torsionally and longitudinally. That projectile is trying to twist and pull the barrel along with itself. It's really impressive to see a super-slow motion of 155mm gun tubes when firing standard HE rounds. It's over so quickly, you just don't see it, literally, in the blink of an eye. Although much smaller, small arms projectiles do the same thing. Interior ballistics is interesting.

I must admit that you are way beyond a guy who grew up on a small farm on Dog Hollow Road

 

[Shooter13]

Like this.View attachment 1345752

Exactly, page 149 of Tony Boyers book, it will not tell you it is too thin just too thick.

 

[gunsandgunsmithing]

I'm not sure I buy the harmonics thing and I'm even skeptical about bolt lugs having anything to do with it but I'll admit to not having a better suggestion. It does seem to be more relative to neck thickness than anything but I have guns that produce it distinctively and others that don't. My winningest gun does not. Go figure.
If it shoots, I'm not sure any of this matters but I am curious. Been trying to figure the relevance of this for many years and bunches of bbls. I can't say that I've ever found anything conclusive.

 

[Dusty Stevens]

I'm not sure I buy the harmonics thing and I'm even skeptical about bolt lugs having anything to do with it but I'll admit to not having a better suggestion. It does seem to be more relative to neck thickness than anything but I have guns that produce it distinctively and others that don't. My winningest gun does not. Go figure.
If it shoots, I'm not sure any of this matters but I am curious. Been trying to figure the relevance of this for many years and bunches of bbls. I can't say that I've ever found anything conclusive.

I used to not buy the lugs thing either til tony told me and i started shooting 3 lug actions. Nothing to do with harmonics and everything to do with neck thickness, and neck tension and how fast the neck seals. No idea how the lugs affect the soot but they do. I just go with it

 

[gunsandgunsmithing]

I used to not buy the lugs thing either til tony told me and i started shooting 3 lug actions. Nothing to do with harmonics and everything to do with neck thickness, and neck tension and how fast the neck seals. No idea how the lugs affect the soot but they do. I just go with it

Me too! One of those things that happens but I'm not sure why as long as it shoots.

 

[Dave M.]

I run .0015 on my 6PPC and BR, .0025 on my 30BR.

I assume you are talking total diametral clearance.

 

[Steve Blair]

Thats a “wave sign” not a sign wave!

 

[gsardokla]

I must admit that you are way beyond a guy who grew up on a small farm on Dog Hollow Road

Just a country boy from S. Oklahoma who's been hunting since age of 6-7 and reloading since I was 15. Graduated from Ok. State and served in US Army, Ordnance corps. One of my mentors was a top dog (at one time) at the BRL in Aberdeen PG. Another mentor was a member the Hiroshima mission - he showed me his own personal pics of the mushroom cloud. He was a shooter, conventional munitions expert, and top marksman. While internal and external ballistics is interesting, my thing was terminal ballistics...and hunting, fishing, and shooting.