the + and -'s of shoulder angles

MagnumManiac said:

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.

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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

Calvin45 said:

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

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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.

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.

Mikecr said:

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.

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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.

Calvin45 said:

I've heard that's a real issue with attempts at 50 degree shoulders

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Even at 45°, shoulders are difficult to form the wider they are.
For example, the 30-06 based 40° & 45° are simple to form when cases are being drawn, move into the 404 or 416 case and the shoulders are wide, which means several steps are required to stop the shoulder wrinkling while being formed. Annealing often is also required. I anneal my 416 brass before it goes into the hydraulic form die, and if you pound on it hard, the shoulder can wrinkle. 2 less than hard blows work just fine.
It takes 2 full power loads to get fully formed sharp shoulders, and even start loads will not form sharp edges.

Cheers.

Calvin45 said:

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.

Click to expand...

I know it's a risk. The cost of a reamer, barrel, & some brass.
My intent is to NEVER bump shoulders (nor collapse them),, and I'll either be successful or not.

The tricky part for me is neck-chamber end clearances.
Forming a shoulder to such a degree will pull necks back considerably.
I will initially have to hydro-form or COW FF, and then trim to fit, as necks must be too long to begin with.
I have a form die set with which I can get pretty close, and I always do a deep body dip anneal before any forming.
Problems depend on the case & cartridge I decide to try this with.
Probably my 26wssm Imp, but I would really like to try it with 260, along with a suspension webbing and front ignition (another efficiency gain).

My life right now has me working like a dog, with experiments collecting dust....
But I do need to get on this.

Mikecr said:

The tricky part for me is neck-chamber end clearances.

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I see your dilemma, even with multiple sizings you'll probably never get anywhere near the end of the chamber.
I chose .030" chamber neck clearance on my 416 Rigby Improved cases, trim my brass .010" short of this, but many firings to get to that point and, I worry about carbon rings. Haven't found one yet that was a concern, but still lingers in my mind.

Would love to see a 60° degree shoulder be successful, but I have an idea on a radius shoulder that would facilitate the same principal, yet not be so radical.

Cheers.

A bud and I have been working with a few single radius shoulder wildcats since the late 90s and early aughts. Very efficient and minimal case growth. The dies are burned (wire EDM) from the same electrode that is used on the chamber. Sizing resistance is very minimal. Top is a 25-284 bottom is a 30-376 Steyr. I also have 6.5 and a 338 based on the 376 Steyr case. In hindsight, I wished I would have picked a parent case for which better brass is available.

ARlife4me said:

given it's formed for that particular firearm, correct.

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This is more important than most realise. Reviewed a beautiful custom .358 STA chambered in a Brevex Magnum Mauser Action.

Sounds good on paper, but wouldn't feed very well as the sharp shoulder on the 358 case was binding on the feed ramp. A good smith should have picked up on this and corrected it, but I later found out that the owner didn't provide cartridges or dummy's to the 'smith.

Lots of conversation about angles and case sizes and ratios trying to find those magic 'golden numbers' which often hide for decades or even longer. Experimentation regarding cases is fascinating, time consuming and money consuming but a ton of fun!

I, like some many others, have been drawn into these challenges with some good results and some disappointing ends. All in all though, the Ackley Improved variation has proven to be the most successful generally. Note generally.

I have found though that I can get better results by using this case with appropriate expansion below the neck:



Please note the neck angle as this is a design from the 50's.

I played with 404 Jeffrey brass for a time before the RUM, WSM or Nosler came out. Results were mediocre because it didn't increase velocity over Weatherby cases.
Then the 416 Rigby case, this thing is as modern as tomorrow and can be used to run right down to 7mm, 6.5mm if your that adventurous, and anything up to and including 458, 470.
I have a 450 Rigby, and have used that brass too, but it's getting difficult to get.
I am still amazed that I have had these since 2000 and the Norma Mag, Lapua Mag and 33/37XC took so long in development. It just made sense to me way back then, just as the RUM was released, which was an innovation in itself, I knew I was onto something grand.

Cheers.

DLJ6 said:

A bud and I have been working with a few single radius shoulder wildcats since the late 90s and early aughts. Very efficient and minimal case growth. The dies are burned (wire EDM) from the same electrode that is used on the chamber. Sizing resistance is very minimal. Top is a 25-284 bottom is a 30-376 Steyr. I also have 6.5 and a 338 based on the 376 Steyr case. In hindsight, I wished I would have picked a parent case for which better brass is available.
View attachment 610791

View attachment 610792

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Those are neat looking. Opposite kind of single radius too the 5mm/35 smc cartridge I've read about (see photo from Wikipedia). That one had a convex radius shoulder, yours has a concave radius. Interesting. That smc cartridge has a real long neck too…

How frequently do you need to trim brass with your design? Just looking at it I'd suspect it'd stretch a heck of a lot more than the convex/SMC type radius or a straight sharp angled Ackley or steeper type shoulder.

Tag

That SMC cartridge inspired my idea, however, the larger the calibre and case size results in diminishing returns of its principal advantages.
You need a wide case and small narrow neck to get what it does, which is to hold back the flame an extended amount.
This would not work on a large case.
I was thinking a blistering fast 17 calibre cartridge, above 5000fps…
Just an idea at this point.

Cheers.