Shoulder Design Discussion?

[Kobra]

As a newbie to this site and a real rookie long range shooter, I have a few questions on various shoulder designs.

First does the radius shoulder of a Weatherby really improve efficiency? Or is the added velocity just the extra powder space this design affords?

Also if Ackley always liked 40 degrees why are factory rounds usually 30 or 35? What do you gain with the 40 degree besides increased powder capacity?

Thanks for the info.

 

[LiMe]

The reazon to the 30 degree, is that it is easier to make brass with that angle... at least, think that i have reed it somewere

just have to say that this is a grate place! haven´t written any, becuse i think that i haven´t any thing to say, but I have learned much by reading the topics here!

Peter

 

[Ken Howell]

"First does the radius shoulder of a Weatherby really improve efficiency?"

No. That old "Powell-Miller Venturi Freebore" (PMVF) shoulder was pretty well discredited before Roy Weatherby became enamored of it and made it a sort of Weatherby trade mark. It has no positive ballistic value that anyone has been able to substantiate.

"Or is the added velocity just the extra powder space this design affords?"

No again. The extra velocity is a result of VERY high pressures in the factory loads. (Long story is too long for here. Suffice to say, I'm privy to some frightening inside-the-industry information that I can't publish without betraying confidences and possibly costing some good people their jobs.)

"Also if Ackley always liked 40 degrees why are factory rounds usually 30 or 35?"

Ackley did NOT always use the 40° shoulder. I haven't run the numbers, but I seem to remember that he used 28° shoulders at least as often if not more often than he used the 40° shoulder.

"What do you gain with the 40 degree besides increased powder capacity?"

Other problems are what you "gain" -- and not enough more powder capacity to be worth the trouble and expense (assuming loads with the same pressure levels in the same cases but with 25°, 30°, and 40° shoulders).

The manufacturers don't like having to make cases with shoulders steeper than 25°, and the maximum shoulder angle for relatively trouble-free handloadling seems to be 30°.

[ 03-05-2002: Message edited by: Ken Howell ]

 

[Dan Conzo]

I don't know about the efficiency of the venturi shoulder but the 300 Wby is one heck of a good case and spawn a lot of outstanding wildcats with and without the venturi shoulder. Nothing beat it (in standard actions) until lately (404, Ultra) which people did play around with years ago but didn't go anywhere. A 30 Ultra vs a 308 Baer from what I've seen is a toss up. If it wasn't for the 300 Wby case, we wouldn't be where we are today with long range. Just an opinion.

 

[jhendri2]

Ken,

A quick question, you stated "the maximum shoulder angle for relatively trouble-free handloadling seems to be 30°", can you explain this further.

I have not had any trouble reloading with AI or SSK (40 degree) shoulders. Also, as stated by Darryl in another thread most large LR rounds are improved to 35 degree shoulder angles.

I thought the steeper shoulders were easier to reload due to less case stretch and my brass normally lasted longer. The rounds I had the most problems with was shallow shouldered cartridges (esp 220 swift) because of case stretch, it seemed like the cases would not last as long.

Am I missing something? Thanks in advance for your help.

Jim

 

[Darryl Cassel]

Hello Jim

We have found at Williamsport that the 300 Weatherby venturi shoulder will give more case stretching then the 30, 35 or 40 degree shoulders. I shoot 300 Wetherbys there and know first hand. Also have the 308 Baer, 30 Goodling and 30Imp Piccarreta and can make the comparison.

Ackley used "Mostly" 40 degree angles on his cases for this reason (case stretching) and also for the ease of headspacing and further improving the case. Problem with the 40 degree seemed for many to be, it created more "back pressure" against the bolt. This too shortened case life with flatened primers and eventual web expansion with full power loads.

Gibbs found this out early on and came with a 35 degree on all his designs and many cases today, 308 Baer, 30 Goodling, 30 Imp Piccarreta are all 35 degree angles and all seem to work VERY well at 1000 yard matches.

For the original poster;
The extra velocity "advertised" in the Weatherby is due to the amount and burning rate of the powder used and more importantly, the excess "Freebore" they chamber their rifle with.
It has been established that, Excess freebore will give higher velocities but will "destroy" accuracy. We as longrange hunters/shooters want all the accuracy we can get. Weatherby found this out too but,even though there are many complaints of terrible accuracy from their rifles, they continue to chamber them with the freebore "feature" anyway. This is especially true with the rifles from the 300 and the 30/378. Accuracy is just NOT what it should be in MOST Weatherby factory chambered rifles.
I know of those who have set the barrels back and eleminated the freebore and they shot fine, even the new accumax 30/378.

The first thing a good gunsmith will do when he chambers a 300 Weatherby or any of the improved versions, is to get rid of the excess freebore and make it so you can seat your bullets near or softly into the lands.
Getting rid of the venturi shoulder and going to the 30,35 or 40 degree also allowed headspacing on the shoulder instead of the belt which again is found to be a better way to go.
You can't "Jump" the bullet into the lands (freebore) and expect excellent accuracy. It just won't happen.

May have got you off the hook on that one Ken.

I agree with my fellow Williamsport member Dan Conzo on the 300/340 Weatherby parent case, as a much used round, straight or improved (without freebore), for 1000 yard match shooting.

Hope that helped.
Darryl

 

[jhendri2]

Darryl,

I agree with everything you stated. I was just wondering why Ken stated that the 30 degree shoulder was easier to handload for than a 35 or 40 degree shoulder.

I wasn't sure if I missed something when I was reloading for improved rounds. Because, as stated before I have had more problems loading shallow shoulder angles due to, as you stated case stretch, than I have with improved rounds.

By the way, I agree with everyone on the "venturi" shoulder as being more of a marketing scheme than an actual product of design to increase accuracy and velocity.

Again, thanks for the help.

Jim

 

[Ken Howell]

My comment about the 30° shoulder is based on bad experience (mine and others') with the 40° shoulder. I have no experience with a 35° shoulder, which seems to me not distinct enough from either the 30° or the 40° to be worth talking about.

Case life ended abruptly, sometimes with the first loading of fire-formed cases, when the cases "turtle-necked" with difficult bullet-seating -- a liability of the 40° shoulder. (The necks didn't accept the bullets but instead collapsed back inside the case bodies -- reversing the shoulders.)

The virtues of the 40° shoulder were born in conjecture that ignored some of the basic physics of expanding high-pressure gas, and through the sanctity of print, shooters adopted this conjecture as proven theory. I studied all this when it was new, and fell for it for a while. Pioneer ballistician Homer Powley explained the fallacies of it -- but the explanations are much too long for this post. So I'm satisfied to simply ignore the 40° shoulder altogether and let those who remain enamored of it continue to enjoy their fantasies regarding it.

 

[jhendri2]

Ken,

Thanks for the explanation of your experiences, though I have never seen this, I can understand how it happens.

Is there a book by Homer Powley, or any articles by him that I can read? If so, where can I get it?

The subject of case design/ballistics has always piqued my interest, any "reading list" material you can provide (other than the common works) would be great.

Again, thanks for the info.

Jim

PS - I hope I didn't offend you with my earlier question, I only asked out of a genuine knowledge search.

[ 03-06-2002: Message edited by: 338Lapua ]

 

[dave7mm]

Ive had Ackley Improved cartridges
(40 degree) since 84 and at last count think I have about 7 of them.Ive never had feeding problems on any of them.And on both of my 22 Cheetahs the case will actually get shorter when you fire form it.Dont need a case trimmer thats for sure
The biggest problem that I have is the cases after a number of firings will get tight in the chamber.The hotter the load you run,the the quicker the cases get tight.Resizing or bumping a 40 degree shoulder is something I've never had any luck with.And thats with all 7 guns.
I've tried dies from RCBS, Redding and a shoulder bushing die from Neil Jones
Custom Products.When you do try to full length size a Ackley case (move the shoulder back). Typically the case wall just behind the shoulder will buckle making for a messed up case and its still tight in the chamber.
Just as an example I've reloaded 6mmPPC cases well over 100 times with a
minimum full length resizing die.The PPC has a 30 degree shoulder and
I've never had problems getting it to move.Or bumping it if you will.
My last new rifle a 25 Booboo based on the 8x68 RWS case has a 30 degree shoulder.
Im sticking with the 30 degree from here on in.
dave

 

[Kobra]

Thanks for the info guys.

My only interest in Ackley's designs was a Ackley 243. Anyone had experience with it?
A Ackley 22-250 was interesting also.

 

[357Mag]

Kobra-

Howdy !

I know this is an older post, but wanted to mention...

In " AI " cartridges, case capacity increase does not come via sharpening of
the shoulder angle. That step in and of itself reduces case capacity ( esp when powder will not be positioned within the neck ).

It's the " blowing out " of the case' shoulder diam ( for example... when part of an AI case forming process ) that provides the case capacity increase over and above the stock configuration.

Combining the two steps should result in some case capacity increase, the amount of which varies w/ the differing cases involved.


With regards,
357Mag

 

[tbrice23]

Yeah, a bit of conjecture and misinformation on this old thread.

 

[dok7mm]

HaHa! I thought I was in the Twilight Zone. The collapsed cases and inability to bump 40* shoulders had me scratching my head. One of these days, I'm gonna start paying more attention to the date on the posts.