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Handloads.Com ForumGeneral DiscussionVenturi
Could someone please explain what the Venturi Shoulder is? I also need to know the pros/cons of the belted case. I find a lot of references to these two items, but it would help if I knew what they were.

Thank You!
Welcome aboard,
According to Weatherby:

"A unique double radius Venturi shoulder design increases the velocity of escaping gases without increasing the pressure within the cartridge. This results in higher velocity within standard pressure ranges."


Someone else will need to answer what the pros/cons of the belted cases are, what I've heard is they're mostly a gimick and don't really give you any advantage.

We’ll raise up our glasses against evil forces, singing; whiskey for my men, beer for my horses

Molon Labe!
As I understand the whys and wherefores of the belted case Holland and Holland developed it for the African market so that the cartridge would headspace properly with the slope shouldered cartridges they developed 300 hh and 375 etc. With the temps encountered there and the dirty cordite powder used then head space got to be aproblem with out the belt. other wise its my understanding it isn't needed ,and I guess all you'ld have to do is look at the Dakota cartridges and the new batch of short fat stuff thats out there.

Edited on 4/28/2003 9:52:57 PM.
The most expensive bullet there is ain’t worth a plug nickel if it don’t go where its supposed to.
To understand a venturi, think of material going through a funnel. In order for a given volume to go through the smaller neck of the funnel(venturi) the velocity of the material must increase paSSING THROUGH THE CONSTRICTION, BUT THEN CAN SLOW DOWN AGAIN ONCE PAST THE CONSTRICTION. tHE INCREASE IN THE VELOCITY OF THE MATERIAL REDUCES THE PRESSURE OF THE MATERIAL AGAINST THE VENTURI(BERNOULI EFFECT) tHIS CAN BE USED TO CONTROL BURNING RATE AND OTHER FACTORS THAT CAN IMPROVE THE PERFORMANCE AND TEMPERATURE OF THE GASSES INVOLVED IN PUSHING THE BULLET DOWN THE BARREL OOPS SORRY ABOUT ALL CAPS. The belt on some magnmum cases adds an exceedingly small amount of strength to the base of the case. It is used as a registration point for headspacing. It can be seen as bragging rights, but adds nothing to the performance of the round. Usually it is added to prevent the insertion of the belted case in a non belted chamber. eg buy my brass or you can't shoot my gun.
Completely irrelevant to this discussion, but a carburetor works exactly the same way. Air is pulled from the air cleaner into the carburetor venturi by the vacuum created by the downward movement of the piston on the intake stroke. As Buddy mentioned, it accelerates as it passes through the venturi. As it accelerates, the air pressure drops in the venturi area. The fuel bowl holding the gas is vented to the atmosphere and there are passages from the fuel bowl to the venturi. Because the air pressure is lower in the venturi, fuel is pushed up the passages to mix with the accelerated air and into the engine it goes. Engine speed is controlled by how much air is allowed to flow through. So there you have it your engine is just a big air pump when it comes right down to it. And there is your trivia for the day.
God Bless
Here's my spin on it. The belt was an easy way to headspace that imparted the need to buy the factory's ammo. So too is the Weatherby venturi case design. It looks nice but serves no useful function. Weatherby velocity improvements(?) were more the result of freebore than anything else. The powders of the era were faster in burn rate than what is available today, and in order to use more propellant the freebore was necessary to reduce pressure. More powerful and higher velocity cartridges are available today that use neither of these design features. A cartridge is nothing more than a gasket that conveniently seals the chamber/bolt interface, and increases of efficiency due to shape are difficult if not impossible to quantify. One demonstrated fact about cartridge design is that the longer the charge length, the hotter the primer must be, so there is an advantage to the short squat cartridges that are being introduced today in droves. Ignition is more consistant as a result. One other issue being researched by SMC^2 is the hemispherical shoulder as a path to increased efficiency. Their cases are also of the short fat variety and Mr McPherson claims the shape enhances ignition by focusing the primer shock at a point beneath the bullet base as opposed to the scattering of the shock wave caused by more conventional designs. He has a patent on the design, the cases are very difficult to form, and who knows where it will lead. It is, in my opinion, a lot of work for a small gain. Perhaps in the future his research will be bourne out and the design adopted, but I'll not hold my breath.
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Handloads.Com ForumGeneral DiscussionVenturi

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