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<blockquote data-quote="Buffalobob" data-source="post: 104272" data-attributes="member: 8"><p>[ QUOTE ]</p><p> I think that buffalobob expressed the thought that everything that happened in the chamber was a chemical reaction. </p><p></p><p>[/ QUOTE ] </p><p></p><p>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. </p><p></p><p></p><p> [ QUOTE ]</p><p> Also do the gases flow, expand or both to make push the bullet? </p><p></p><p>[/ QUOTE ] </p><p></p><p>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 </p><p></p><p> [ QUOTE ]</p><p> All rifle cartridges are convergent nozzles which have an upper limit of rate of gaseous flow. </p><p></p><p>[/ QUOTE ] </p><p></p><p>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.</p><p></p><p> [ QUOTE ]</p><p> convergent-divergent nozzle </p><p></p><p>[/ QUOTE ] </p><p></p><p>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.</p><p></p><p></p><p>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.</p><p></p><p>My thoughts on the case in question all just revolve around fluid flow. There are other considerations in the world.</p></blockquote><p></p>
[QUOTE="Buffalobob, post: 104272, member: 8"] [ QUOTE ] I think that buffalobob expressed the thought that everything that happened in the chamber was a chemical reaction. [/ QUOTE ] 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. [ QUOTE ] Also do the gases flow, expand or both to make push the bullet? [/ QUOTE ] 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 [ QUOTE ] All rifle cartridges are convergent nozzles which have an upper limit of rate of gaseous flow. [/ QUOTE ] 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. [ QUOTE ] convergent-divergent nozzle [/ QUOTE ] 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. [/QUOTE]
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