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speedygonzalez
Reply with quote  #1 
Speedy: I've followed your writings for a number of years, and respect your opinions ( I also do not "like" or use moly: tried it/ more disadvantages than advantages), and would look forward to your thoughts concerning shoulder angle. Does the angle of the case shoulder have any bearing on throat erosion? I'm thinking of the 243 Win. with the 20 degree shoulder, and a proven barrel burner, as opposed to a similar round with a 30 degree angle, for example. Some believe the sharper angle keeps the "turbulence point" closer to the confines of the case neck, and "short" of the throat area. Thanking you in advance. Frank D. Shuster at: fdshuster@hotmail.com
__________________
Frank D. Shuster

The fundamental principal of exchanging stored chemical energy of a propellant into the kinetic energy of a projectile is through the generation of gas and it's accompanying pressure rise. These gas laws then lead us back into the standard principles of fluid dynamics and laminar flow and turbulent flow but forward flow non the less.
The theory that the individual grains of powder are focused in a specific area because of the shoulder angle or length of the neck thus causing increased throat erosion are quite humorous. If you think if the case neck as a length of barrel the powders are forced forward just as the bullet leaves the barrel of the firearm itself. the turbulent flow inside the case itself would be theoretically increased as the shoulder angle became greater as in an improved case....food for thought their boss!
Now lets open up the forum for greater discussion.

Good Shooting,
Speedy Gonzalez

spclark
Reply with quote  #2 
Is it possible that it's not so much direct impingement of particles - the sand-blast effect - as it's some phenomenon of focusing shock waves?

In a long neck cartridge having a relatively sharper shoulder angle, the shock waves impact inside the case neck. Shorten the neck or reduce the shoulder angle, the point of focus moves toward the case mouth until it moves out of the neck entirely.

I'm no physics expert but I'm aware of how substances can be affected by forces other than direct contact.
speedygonzalez
Reply with quote  #3 
Ineresting theory! Maybe someone else will expand upon it. Curious though that we don't see the damage occur inside the neck of those longer length cases. I can fire a single 6ppc case until I wear out the barrel if I so choose and nothing happens to it as you see take place in the barrel.....HMMMMMMM.
Now you really opened up a can of worms boss!
Where is nine fingers Jackie Schmidt when ya need him?
spclark
Reply with quote  #4 
I've always favored the hot gas theory myself but the idea of a shock wave effect occurred to me once I'd looked at your drawings.

I'm not too confident the nature of burning propellant produces such waves, but the simple act of a primer going off excites vibrations in a rifle action / barrel that are only compounded once the propellant ignites and the bullet begins its travels.

Lots of stuff going on in a Very Short Timeframe, all of which would need close monitoring & quantization (sp?)....

Brass behaves differently than iron alloys both chemically & physically so a direct comparison between brass and chamber erosion isn't a simple endeavor.
speedygonzalez
Reply with quote  #5 
HERE YA GO BOSS!

BRISANCE(PRIMER):is a measure of the rapidity with which an explosive develops its maximum pressure.

In addition to strength, explosive materials display a second characteristic, which is their shattering effect or brisance (from the French briser, to break), which is distinguished from their total work capacity. This characteristic is of practical importance in determining the effectiveness of an explosion in fragmenting shells, bomb casings, grenades, structures, and the like. A brisant explosive is one in which the maximum pressure is attained so rapidly that a shock wave is formed, and the net effect is to shatter (by shock resonance) the material surrounding or in contact with the supersonic detonation wave created by this explosive. Thus brisance is a measure of the shattering ability of an explosive.
Rust
Reply with quote  #6 
Without direct observation to produce empirical evidence it's all theory and I don't know of any direct observation of the internal combustion process in a case or barrel.

Until such time as such empirical evidence is actually developed I'll just stick with the general thoughts of one P.O. Ackley. Short and fat is better, less taper is better, sharper shoulders are better, longer necks are better.

It would be interesting to examine the barrels of that virtually no neck .30 wildcat based on the BR case that Al Nyhus developed with Stan Ware though.
Tommie
Reply with quote  #7 
For years I have wished that someone with more time and money than I would conduct a controlled experiment on this very subject. The problem of throat erosion is most pronounced in cartridges of low expansion ratios and I don't know if typical short-range BR type chamberings would provide the best study. I've always thought a side-by-side involving a .220 Swift and a 40* shouldered 22-250AI would be extremely interesting.

I have read several theories on both sides of the argument and have come to the belief (not "knowledge") that sharp shoulders and/or long necks do provide some level of throat life advantage.

Tom

p.s. despite great temptation, I didn't quote P.O. Ackley
cwood3
Reply with quote  #8 
So what is the limiting factor on shoulder angle? If a little is good a lot is better? Why not square it off? Like an orifice plate in a pipe ? Hmmm, I need to digest this a bit more to have a feel for it.
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