B F - I'll offer "an" explaination, not necessarily "the" explaination. There have been a lot of experiments to obtain more choke effect than is available with the typical 0.035" to 0.040" constriction usually refered to as "Full." Tighter constriction is usually counter-productive. Constriction profiles other than conical have not been proven to work. So, the choke of a convergent section followed by a divergent section may be such an experiment. I'm of the opinion that shot "flows" through the choke as a fluid and follows fluid dynamics principles. If so, the shot column would experience a gain of velocity and a lowering of internal pressure as it passes through the convergent section (venturi principle). The lowering of internal pressure would result in less "spring apart" of the pellets. From a fluid dynamics perspective, the shot is at some state resembling "sonic" velocity at the 0.040" constriction and will not shed any more pressure with further constriction - it will actually regain some pressure. However, if a sonic fluid transitions from a convergent section to a divergent section, it will continue to accelerate as it continues to loose pressure. This is the rocket nozzle principle. I don't yet know if it works that way, but would dearly love to see some comparison patterns from the two barrels. I'd bet that rather than trying for a more open pattern with the divergent section they were trying for greater choke effect.
Any chance you could do some patterns?
Last edited by Rocketman; 05/04/07 11:27 AM.
