Home Forums Hunting & Shooting Ask The Gunwriters Shoulder Angles And Throat Erosion

Ackley opined that the sharper shouldered cases kept the hot powder gasses inside the case and therefore reduced throat erosion as compared to cases with a slight shoulder angle such as the .300 H&H. Is there any practical truth to this?
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<br>Also, haven't the newer powders and more modern steels used in barrel making made more of a difference reducing throat erosion than anything?
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<br>Shouldn't bullet "fit" also be taken into account?

This often-cited and popular misconception doesn't jibe with certain facts of gas physics.
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<br>(a) The molecules of the expanding powder gas ricochet off each other (and the case wall) at about 1,400 ft/sec. NOTHING is going to hold them back, once the bullet gives way before them and starts moving.
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<br>(b) The gas is EXPANDING under increasing pressure, not flowing at an unchanging low pressure like pipeline gas.
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<br>Some of the popular misconceptions about the "flow" of powder gas through the neck of the case may be true ONLY if the neck constriction were significantly smaller than a much larger bore ahead of it -- but this isn't the situation in a chambered cartridge. The gas forced through the constriction of the neck STAYS constricted as far as diameter is concerned. At any given instant, the gas behind the moving bullet is exerting exactly the same pressure upon all surfaces of its confining vessels (case and barrel). That pressure increases, then decreases, from instant to instant, of course, but it's never x in one place while it's x minus y or x plus y in another place.

But part of the "cleaning" axiom is agitation (CATT= concentration, agitation, temperature and time). Some think that less energy or agitaion will hit the throat if the shoulder is sharper. I am not sure about this but it's part of the longer neck = less errosion theory.
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<br>Ken, can you tie this in with the article in Precision Shooting "A New Look At Cartridge Internal Ballistics by Robert Smalley in the May 2002 issue? This article indicates that something is going on different when the primer ignites the powder in gradual shoulder cases vrs ones that are quite steep. That author by the way suggests an elliptical shoulder!

Ken; What about the pressure waves that can cause "blow ups" with the slow powders?. There must be a variation in the pressurer profile.
<br>Good Luck!

The very little that I know about the "wave" theory as applied to the expanding, propelling gas doesn't jibe with what I know about the known nature of the gas's high-pressure expansion. So until I understand it better -- well enough, possibly, to accept it and apply it -- I don't buy the notion of waves coursing through the cloud of gas.
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<br>I have another theory about what causes ultra-light loads of slow powders to burst a rifle now and then. When I have the means to build the necessary test apparatus, I'll check it out -- and publish the results. For now, however, quite a number of far more important (and more interesting) projects have first dibs on my paltry dollars.