Double Radius vs Straight Taper Brass

[FrankieJames7]

i am wondering why weatherby made ammo with a radius in the brass shoulder instead of the standard straight taper. i am guessing it doesn't erode the throat as fast or leads to more precise groups. just curious

 

[sable tireur]

Actually, it has to do with the transition of a solid into plasma. Plasma is one of the states of matter; solid, liquid, gas and plasma. When the powder is ignited by the primer, a superhot gas or plasma is created. The radiuses in the shoulder allow that plasma to transition smoothly into the neck to propel the bullet down the barrel. The velocity of that plasma is increased by that smoothness in the transition.

The angular shoulder is more abrupt in the transition of the plasma but much easier to form during the making of cases.

I'm sure there's a science geek who can add many more details to this.

 

[FrankieJames7]

that is exactly the kind of answer i was looking for. the world of modern engineering, love it. now i never have to ask this question in my brain ever again

 

[Deleted member 46119]

The Weatherby double radius was used for a long time in long range target shooting. So was the 300WM.

Then came the larger Jeffery 404 based beltless magnums. The belted dropped away. The double radius was tried in these but seemed to offer no advantage.

I am a Weatherby dude. I keep lots of rifles chambered with the double radius belted magnums. Tradition more than anything else.

 

[J E Custom]

There are several reasons that Weatherbys have a double radius. the first was that Roy Weatherby was trying to get the most velocity, and from an engineering standpoint this should help for the reasons that sable tireur mentioned. and also he believed in lots of free bore to lower pressure and allow more powder.

The freebore worked but the double radius appears not to have made any difference in the efficiency. In fact it appears to have diminished the powder efficiency compared to some straight tapered designs. When you take a standard Weatherby chamber and change only the radius shoulders to straight angles (35 to 40o) and leave the freebore and lead angle the same, it appears to improve the efficiency by needing less powder for the same velocity.

The short magnums are a good example of the efficiency of the straight shoulder angles and a shorter powder column. I have many Weatherby chambered cartridges and like them but I have not seen any improvements in throat erosion over standard cartridge rifle barrels.

Not everything in theory works like it should, so until it is proven it is still just theory.

Just a note; If the radiuses were better, the 6 PPCs and other bench rest cartridges all the way up to the Chi Tacks would all have them.
Again, I have some very accurate Rifles using Weatherby cartridges but I also have some very accurate rifles in non Weatherby cartridges
so the radiuses are more of a trade mark of the Weatherby cartridges
than anything else in my opinion.

J E CUSTOM

 

[sable tireur]

I'm sure there's a science geek who can add many more details to this.

See what I mean...

This is the description I got from a Hydraulics Engineer when it came up in a discussion about the very same shoulders, maybe 25 years ago, although the time frame doesn't matter. It is simple in form but is truthful in the effect.

Plasma and fluids, such as the heated gas from gunpowder in a cartridge case and water in a water line, can and will act similarly when the water line or cartridge case is reduced in size using radiuses in the reduction joint. This can and will increase the velocity of the water or the plasma.

Now, is this a significant effect in the Weatherby cases? Probably not, although it does takes place. The downside, as pointed out, is that the plasma and unburned powder escapes the case smoothly but without the efficiency of running into a sharply angled shoulder.

One of the keys to using 30° to 40° shoulders is the reflection of the unburned powder back into the heat which is igniting that unburned powder, thereby increasing the efficiency of the charge being used. More powder burns in the case as opposed to burning with less efficiency as it's being propelled down the barrel.

Regards.

 

[Edd]

A case with a straight shoulder also has a double radius. The ones on a Weatherby case are just closer together.

I knew someone that would put coloring in their race car fuel. I know why they did that. I think Weatherby did his shoulder for the same reason.

 

[MudRunner2005]

It was purely a marketing gimmick to create his own proprietary brand of cartridges for his proprietary rifles. Nothing more, nothing less. It was a capital endeavor...Chasing the green.

People can talk all the scientific crap about a Venturi radius'd shoulder being better, but it's proven the low wall taper cartridges (think Ackley Improved) with the 40º-50º straight-taper shoulders are nearly identical in function and efficiency.

 

[Buffalobob]

In fluid mechanics, as was described earlier, there are two type of flow, laminar and turbulent. In the mid 20th century the state of science was that we knew laminar flow was more efficient energy wise than turbulent flow. Sharp corners induce more turbulence than radius-ed shoulders therefore there is more internal energy loss of the fluid flow. I remember the old NASA induction scoops on the mustangs where the design was to induce laminar flow. The same principles are used in car headers and intake runners as well as household plumbing - no sharp corners.

As science and understanding advanced, we found there are places in cars where turbulent flow is better than laminar flow and thus we see the Blue oval Turbo swirl heads and the Bowtie tumble flow heads because you get improved mixing of the gasoline and air. I even had a pair of aluminum turbo swirls at one point in my life. So in a cartridge case if you simply analyze the mixture of powder granules and gas as a fluid then you will come to the conclusion that radius-ed shoulders are more energy efficient in moving gas out of the cartridge and into the barrel. However if ignition is not uniform in the powder and you analyze the mass as two separate fluids then you are into the same issue as Ford and Chevy and need to induce turbulence (mixing) which means disrupting laminar flow in order to gain mixing and uniformity of the blend.

It is logical as a physicist and an engineer to assume that Roy W at the time he developed his cartridges understood the science of combustion in a cartridge case about as well as Chevy and Ford at that time understood combustion in a cylinder. We have come a ways in half a century or so both in cartridge case design and cylinder head design. One of the things we can conclude is that science moves on along and we learn more and more. It is not at all clear to me that we have a very full understanding of the internal dynamics of a cartridge even today ( I admit I don't keep up with it and it was never my area of scientific focus).

 

[FrankieJames7]

A case with a straight shoulder also has a double radius. The ones on a Weatherby case are just closer together.

I knew someone that would put coloring in their race car fuel. I know why they did that. I think Weatherby did his shoulder for the same reason.

the "just cause i could" reason is a good one. it is often the reason for many of my own actions in life, just cause i could lol

 

[J E Custom]

Here are some comments from Weatherby rifle website. these guys live and breathe Weatherbys and there comments are very similar to ours.

http://castboolits.gunloads.com/archive/index.php/t-127486.html

More opinions on the double radius.

J E CUSTOM

 

[Sral1987]

The differences to this are all too minor to spend time about this nonsense. All these new cartridges are about money making thats it.

 

[Mikecr]

Forget 'flow'. There is practically none until the bottle uncorks.
What does improve efficiency is holding the powder charge back, ideally burning near 100% in the chamber.
Ackley Improvement and short/fat designs function toward that.