the + and -'s of shoulder angles

[Calvin45]

To answer this simply as someone that designs my own cases, YES, shoulder angle and case taper matter, not just for the brass, but for the chamber throat too.
Minimum case taper to stop ANY chance of sticky extraction, has been tested to be .005" per inch. Ackley is .010" per inch.
Shoulder angle does 2 things, the steeper it is, the less case growth you get and it holds the flame front longer inside the case and protects the throat/leade for longer. Even straight walled cases have a minimum case taper parameter.
Neck length is also a consideration in conjunction with shoulder angle.
30° is useless for throat protection, 35° does provide SOME throat protection, 40° definitely protects throats with neck length minimums and 45° provides maximum protection to the throat with neck length optimums and cases hardly ever stretch.
The ONLY difficulty with these shoulder angles is the fact that sizing them becomes difficult as the brass resists and springs back to memory, so annealing is necessary every firing.
If you understand these difficulties first, then have your dies made, there should be no clickers and other such issues.

Cheers.

Mr. Maniac sir!!!!


I'm trying to remember if I was you i was talking with a while ago about this, but either way….what's your take on the + and - of the curvy weatherby double radius shoulders, while we're talking about shoulder and case geometry anyway it seems relevant and hopefully not too derailing. You do seem to know a lot and have a fair bit of experience with gathering experimental data from this field of research.

I personally do not think that it's only a gimmick or just for the sake of being different/proprietary. If nothing else it allows for a "net" sharp shoulder angle that still feeds from a magazine like a greased sausage! . I don't know that I buy Roy's claim that it makes anything faster, but at the same time my own limited experience with the .257 weatherby just floored me with how unbelievably forgiving that cartridge is, against all odds. It ought to be a fussy pig, with its goofy shoulder, headspacing on a belt, gobs of freebore, and massively overbore capacity. But it just plain isn't. It was almost like magic how easy it was to tune and find multiple loads it loved. Maybe the shoulder had nothing to do with that, but I'm curious what you have to say

 

[MagnumManiac]

Mr. Maniac sir!!!!


I'm trying to remember if I was you i was talking with a while ago about this, but either way….what's your take on the + and - of the curvy weatherby double radius shoulders, while we're talking about shoulder and case geometry anyway it seems relevant and hopefully not too derailing. You do seem to know a lot and have a fair bit of experience with gathering experimental data from this field of research.

I personally do not think that it's only a gimmick or just for the sake of being different/proprietary. If nothing else it allows for a "net" sharp shoulder angle that still feeds from a magazine like a greased sausage! . I don't know that I buy Roy's claim that it makes anything faster, but at the same time my own limited experience with the .257 weatherby just floored me with how unbelievably forgiving that cartridge is, against all odds. It ought to be a fussy pig, with its goofy shoulder, headspacing on a belt, gobs of freebore, and massively overbore capacity. But it just plain isn't. It was almost like magic how easy it was to tune and find multiple loads it loved. Maybe the shoulder had nothing to do with that, but I'm curious what you have to say

Ok, Roy looked at his design and quoted the radius shoulder acted like a velocity stack, which is a common device shown in fluid dynamics to improve gas/water flow by creating a negative area allowing more volume than what the stack actually contains, 110% is quite normal when measured.
Now, this has never been proven or disproven to do anything in a rifle cartridge. However, testing of throat erosion shows the radius shoulder, neck length and long freebore plays a part in reducing throat erosion, but if you trim the neck back, it is less dramatic and throat erosion goes up.

The Pressure Trace shows the Weatherby design has a gentle start pressure that rises slowly to max pressure for a considerable time curve, whereas other designs with slow gentle tapers rise abruptly. The Ackley shows similar results to the Weatherby, those with long necks appear to be more efficient in regard to grains of powder burnt to velocity obtained.
Decreasing body taper appears to be the biggest gain in efficiency, especially with large cases, which is why the RUM works so well.
The 416 Rigby Improved case, holding up to 125g of H50BMG, is the highest grain powder per velocity gain I have ever seen.

So, yes, the Weatherby radius shoulder is not a gimmick, but it has never been proven to allow more gas flow, however, it does hold the flame front back in the case for longer.
I still can't believe how high I can push my 270 Weatherby without excessive pressure, it is phenomenal.

Cheers.

 

[Mikecr]

I'm considering 60deg shoulders for my next chamber.
Not only for efficiency, but to hopefully eliminate a need for shoulder bumping.
It's my last holdout to eliminate ALL sizing.

There is another factor that comes into play as far as improvement gains: body length to width ratio.
This was a consideration for the WSSM case before Winchester applied a lot of bad decisions to it.
But their basis was right. Short/Fat is definitely more efficient.
Flipside 30.06 for example, with it's long narrow body, cannot run efficiently no matter what you do to improve the case shape.
In QuickLoad, the adjustment for case ratio efficiency (bottlenecking) is called 'weighting factor'. When you calibrate QL to your results, weighting factor can be useful and telling of efficiency.

If you begin with a reasonable capacity for cal, and improve the case to hold more burning/pressure back in the chamber, you will likely see an efficient design. With sufficient breech support and minimal chamber clearances, you can jack up pressures (with an improved case) to gain even more efficiency. Powder loves pressure.
If you think you could just use faster powder for this, you're wrong. You'll lose load density and get very peaky pressure curves, instead of flattening plateaus. If you think you can just burn more powder, you're wrong. You will never gain efficiency with excess powder.

 

[Calvin45]

I'm considering 60deg shoulders for my next chamber.
Not only for efficiency, but to hopefully eliminate a need for shoulder bumping.
It's my last holdout to eliminate ALL sizing.

There is another factor that comes into play as far as improvement gains: body length to width ratio.
This was a consideration for the WSSM case before Winchester applied a lot of bad decisions to it.
But their basis was right. Short/Fat is definitely more efficient.
Flipside 30.06 for example, with it's long narrow body, cannot run efficiently no matter what you do to improve the case shape.
In QuickLoad, the adjustment for case ratio efficiency (bottlenecking) is called 'weighting factor'. When you calibrate QL to your results, weighting factor can be useful and telling of efficiency.

If you begin with a reasonable capacity for cal, and improve the case to hold more burning/pressure back in the chamber, you will likely see an efficient design. With sufficient breech support and minimal chamber clearances, you can jack up pressures (with an improved case) to gain even more efficiency. Powder loves pressure.
If you think you could just use faster powder for this, you're wrong. You'll lose load density and get very peaky pressure curves, instead of flattening plateaus. If you think you can just burn more powder, you're wrong. You will never gain efficiency with excess powder.

60 degree shoulder???? Holy smokes man, how would you go about doing that without just collapsing the shoulder entirely, I've heard that's a real issue with attempts at 50 degree shoulders…never heard of anyone going for 60!

But that's how we learn things, and I love experimentalists and envelope pushers and am super curious how this all goes for
You and what you discover. Hope you do this and share your results here.