I hear tell of this phenomena, but dont understand how it works and, how it pertains to case design. Are there existing cases that use this feature, and is it a worthwhile advantage?
Sorry if this is old hat to you guys.
boet

I don't know if this has any value --
i think of it as the neck of a jet engine.

This was Ralph Millers invention of the 1940's which used a blown out 300 H&H with a long throat, the venturi shoulder is a double radius the opposite form of the weatherby cases, concave instead of convex. I believe the original cartridge was name the 300 Miller freebore, later he picked up a partener and they made a few changes and renamed it the 300 MPFV or some such. I believe this is where Roy Weatherby got his ideas from, think they haled from the same neck of the woods. I've got info somewhere on it's creation.

The venturi effect is another version of the Bernoulli Effect, which states that a faster moving liquid or gas has less pressure. You can see the Bernoulli Effect for yourself by tearing off a strip of paper and holding it to your chin and blowing over the top of it. The paper will rise up because the faster moving air has less pressure than the air underneath it, so it rises. (this is the reason airplane wings work, the curved top surface of the airfoil is makes a longer path for the air to follow as opposed to the relatively flat underside of the wing).

Now a wing is just one surface, imagine a tube where the gas or liquid is encircled so it has to flow faster through the restriction. That is what the venturi effect is. It is the common principle for virtually all carburetors and siphon spray guns.

Now what advantages it offers for cartridge case design I cannot say!

quote:

Originally posted by swheeler:
This was Ralph Millers invention of the 1940's which used a blown out 300 H&H with a long throat, the venturi shoulder is a double radius the opposite form of the weatherby cases, concave instead of convex.

I believe the Miller shoulder has only the single radius. Weatherby added the second radius, and a lot of hype.

These are venturi shoulders.

Ray

quote:

Originally posted by Cheechako:

quote:

Originally posted by swheeler:
This was Ralph Millers invention of the 1940's which used a blown out 300 H&H with a long throat, the venturi shoulder is a double radius the opposite form of the weatherby cases, concave instead of convex.

I believe the Miller shoulder has only the single radius. Weatherby added the second radius, and a lot of hype.

These are venturi shoulders.

Ray

Ray you are probably correct, I believe in late 80's a gunsmith showed me a 25-308Norma venturi shoulder he had chambered up for someone, would imagine 257 webby performance. I think Brian Sipe ended up buying all his reamers and it no doubt is just collecting dust now. What's the triple c stand for?

CCC = Controlled Combustion Chamberage.

PMVF = Powell Miller Venturified Freebore.

Ray

quote:

Posted 14 January 2009 21:17 Hide Post
I don't know if this has any value --
i think of it as the neck of a jet engine.

i sort of think of it as snarfing down your beer so fast that it causes a giant burp

It is simply a nozzle which improves gas flow into the throat (of the nozzle). There is no 'venturi' in a rifle cartridge. A venturi has a recovery section (where pressure is recovered in the divergent portion of a nozzle), while in a cartridge, the gas has nowhere to go as it is being trapped by the bullet. It is a convergent nozzle and it will assist in gas and unburned powder granules entering the bore behind the bullet thereby lowering the pressure in the case a little (gasses flow from higher to lower pressure). It allows the shoulder to be shorter than a straight taper.

Any good phisics book will give you a good definition. roger

quote:

Originally posted by bartsche:
Any good phisics book will give you a good definition. roger

That sounds like work and we all know work is a four letter word

Venturi used it to steal water from the city
of Venice. They billed on the size of the main
feeding water. He put a constriction in the pipe. Not the last crook to become famous.
Good luck!

For a number of years the carburetors on motorcyles were designed in a venturi configuration.

I have a vague recollection of another definition of "venturi effect"

As the bullet exits the muzzle, the powder gas, leaving the barrel faster than the bullet, blows past the bullet, and this wind was thought to increase the velocity a bit. After some testing, it was decided that any increase in velocity was insignificant. And this was called the 'venturi effect".

Or some such.

Does anyone remember anything like this?

RG