Roy , I read an article somwhere that discusses this same idea , even had some of the same photos. I'm sure that on paper and on the cumputer screen that its a great setup but in reality I don't think that it will make such a huge differance. it has alot to do with than just shoulder angle and shape or the Weatherby line would be more popular., it has to do with the case lenght to the bullet base, that why so far only small caliber have been worked with , it would take like a 50BMG case or somthing to make this work with a 30 cal bullet.
Ralph Payne made a round back when that was sort of the same idea , it was called the 7mm Venturan , it was a short Mag cas with a radiused shoulder , supposidly got close to 3300fps with 160 class bullets
I also had a friend that did this kind of round , it was a 378Wby case shortened to 2.25" and necked to 7mm , he got to 3300fps with 160 class bullets and 80 odd grains of 4831 , barrel life was short and the velocity was not what he expected. He got his idea from the 30-378 Arch which is the same case but has a standard shoulder around 30 degs instead fo the radiused one that my buddy used.
Its hard to get ones head around but their is a reason that some of the same case desgines have been around for so long , for as long as bullets have been stuffed into brass cases guys have been trying to get more out of their guns , guys like Parker O. Ackley , Dr. E.L. Arch , Fred wade , Ralph Payne and our very own Kirby Allen have streched , pushed formed stuffed and worked trying to get the very most out of a long range gun
Somewhere in my computer a few month I wrote up a long discussion on this and then decided not to post it because it was so negative.
JD hits the same points in only a few sentences. Being as Alabama lost in the second round I guess I have some time. The Weatherby double radius is simply a venturi orifice. It has less pressure loss than the regular angled shoulder cartridges if the distance from the shoulder to the neck is the same. Burning powder and gas will flow smoother through the curved constriction than the sharp angled constriction. You can check any hydraulic pipe fitting manual on pressure headloss. Check thehead loss of flow meters in a irrigation system. Same thing goes for air flow if you should happen to have any mechanical engineering references around. Out in the field you will see Parchal and Palmer Bowles and verturi flumes for measuring irrigation water although simple wiers are the most common. In any event it does not matter what kind of flow you are measureing the curved "appraoch" to the constriction is best for reducing headloss.
I am sure the reason the the case in question has only one shoulder curve is because Weatherby has patented the double curve. A case where half a$$ed is only half as good as full a$$ed. A little funny joke there being as I like Wbys.
So what has the guy invented - a runty half a$$ed Wby.
Now then what does it all mean. Not much is my opinion. I think the guy was bored and decided that here was something that nobody else had done and he did it. Now all that is left is for somebody else to take a case and have the first approach constriction angled and the junction with the neck radiussed. The minor reduction of inside case pressure is not really going to reduce case stretching very much and all this about sparks flying around inside the case ignores the basic principles of the physical universe. Two pieces of matter cannot occupy the same space at the same time and you cannot make sparks and presusre waves fly through a case that is full of powder and focus in the neck.
If this response insults anybody I will be happy to delete it. I try not to post very many "negative remarks" and that is why I never posted my thought before.
It's been quite a while since physics class, but I'm thinking the powder wouldn't allow a "shockwave" to occur as in the drawings. The burning powder should contain the wave and disperse the effects. I would think hydraulic action of the shoulder would have greater influence on the burn than the "shock wave" would. just my opinion.
Beware the fury of a patient man....
In the image linked, I don't understand how what is being shown is being explained. The powder can't begin burning at the base of the bullet can it?
I think that buffalobob expressed the thought that everything that happened in the chamber was a chemical reaction. I look at the moment of initial ignition as combination of chemical (if that's what a controlled explosion is) and mechanical reactions.
Igintion happens, powder burning begins at or near the flash hole followed by mechanical movement of unburned powder and bullet into the bore, if you haven't crimped the bullet as with the hornet. Then powder continues to burn beyond the chamber as the bullet progresses toward the muzzle.
Shoulder angle/curve seems to be designed to deflect the expanding gas and moving powder onto the neck of the case rather than onto the throat.
Am I correct in believing that all the powder does not burn in the case? If not, why not? I'm thinkingto Kirby's powder bridging discussion.
Also do the gases flow, expand or both to make push the bullet? It seems that expansion it the prime mover as I can see the muzzle flash which appears as a flow of gas, which doesn't seem to have much velocity.
My only studies/experience has been with steam turbine nozzles. All rifle cartridges are convergent nozzles which have an upper limit of rate of gaseous flow. Weatherby's idea, hasn't their patent expired, seems a new twist but its still convergent.
To gain any addtional gaseous velocity advantage one would have to design a convergent-divergent nozzle, pretty much like the space shuttle main booster engine has. It would be easy to design but would be one helluva task to rig up an action to handle it. Talk about case extraction problems. [img]/ubbthreads/images/graemlins/grin.gif[/img] [img]/ubbthreads/images/graemlins/grin.gif[/img]
I may be the slowest guy on the mountain . . . . but . . . . I'm on the mountain!
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I think that buffalobob expressed the thought that everything that happened in the chamber was a chemical reaction.
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My thought is that you are pushing a "fluidized bed" of hot gas and granular pellets through a constriction we call a "neck". For a given approach length (shoulder to neck distance) a venturi is better than a hard angle and this can be proven from fluid mechanics. Powder bridging is more likely to occur with the angle than the radius. And more likely to occur with a short "appraoch" and a high ratio of constriction (large diameter body, 40 Degree shoulder and narrow neck- extreme example would be a 40 degree shoulder on a 50 BMG necked down to 17 caliber). The job of the approach to a constricted area is to try to acheive laminar flow and reduce turbulence if you want to get the least amount of pressure inside the case and get as much of the burning to occur in the barrel as possible.
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Also do the gases flow, expand or both to make push the bullet?
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There is gas in the voids of the powder granules. This gas is just regular air but a gas nonetheless. The primer spits out some fire which is a solid that is being converted to gas via exothermic reaction (burning). This causes there to be more gas in the case and the hot gas ignites powder at the base of the case and for a distance through the case. This powder ignition also creates gas. Pressure increases uniformly in the case in all directions even though there are powder granules in the case and at some point the pressure exceeds the neck tension on the bullet and it begins to move down the barrel and gas and granules "flow". The resistance to flow by the friction of the case wall and approach to the neck is determined by several things, one of which is the shape of the shoulder area. The other principle controlling factor is the length of the approach and it is greatly more important than the shape. Sharp shoulders are short shoulders and short vs long is maybe 5-10 times more important than curved versus angled. Long curved is (from a fluid flow standpoint) greatly better than short angled. The reason people like Ackly-ed cases is that the sharp short shoulder resists flow and the gas impacting on it drives shoulder into the chamber shoulder wall creating a flatter pont of resistance to body growth. So we see flow resistance can be our friend for some purposes and our enemy for others
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All rifle cartridges are convergent nozzles which have an upper limit of rate of gaseous flow.
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That is correct (except for the straight walled cases) and what I am saying is that the curved approach causes the upper limit of flow to be higher than an angled approach.
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You do not want a convergent divergent neck. Convergence build up pressure from trying to squeeze through the constriction. You want the least amount of convergence possible and you want it as smooth as possible if you are trying to gain maximum veloicty. The 22 hornet case is the best fluid flow case I know of because it has a very very long shallow approach to the neck. A straight walled case such as a 45-70 has zero convergence and is from a fluid flow concept the very best, but it has a limited powder capacity.
Think about a 50 BMG with a constriction of 17 REm and then back to 50 caliber. You would have so much friction loss trying to get the hot gas and granules through the cosntriction that I would guess you would lose more than 25% of your barrel pressure and velocity. The reason a rocket ship has a constriction is to build up extreme pressures against the rocket ship not against the outside world which may be a vacuum. The cone just gets the hot burning rocket fuel away from the base of the rocket and helps with turbulence and directional stabilty.
My thoughts on the case in question all just revolve around fluid flow. There are other considerations in the world.