Sine waves
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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 would think it's a big ass explosion in the chamber that causes sine waves.
powderbrake
Gold $$ Contributor
Because the barrel is vibrating at its "natural frequency", which is set by it's shape and mounting.
Post #3 says it's also based on the bullet going down the barrel.
An interesting read on the sine wave in barrels:
Cast bullets;
Neck clearance can be changed with bullet diameter... independent of,case neck thickness.
IOW's;we can run the same load pressure,same annealed state,same jam,alloy,etc...and by changing neck clearance with bullet diameter,see the wave come and go.
WRT jacketed; gut reaction is, set your clearance carefully. Too many "little things" to make a blanket statement that there must be "X" clearance.
Neck clearance can be changed with bullet diameter... independent of,case neck thickness.
IOW's;we can run the same load pressure,same annealed state,same jam,alloy,etc...and by changing neck clearance with bullet diameter,see the wave come and go.
WRT jacketed; gut reaction is, set your clearance carefully. Too many "little things" to make a blanket statement that there must be "X" clearance.
jackieschmidt
Gold $$ Contributor
I run .0015 on my 6PPC and BR, .0025 on my 30BR.
Dusty Stevens
Shiner
Thats a “wave sign” not a sign wave!
timeout
Silver $$ Contributor
I must admit that you are way beyond a guy who grew up on a small farm on Dog Hollow Road
Shooter13
Gold $$ Contributor
Exactly, page 149 of Tony Boyers book, it will not tell you it is too thin just too thick.
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.
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
Shiner
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.
I assume you are talking total diametral clearance.
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