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Shoulder Design Discussion?

 
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  #8  
Old 03-06-2002, 10:27 AM
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Join Date: May 2001
Location: Stevensville, Montana
Posts: 14
Re: Shoulder Design Discussion?

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.
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  #9  
Old 03-06-2002, 10:48 AM
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Join Date: Oct 2001
Location: Altus, OK
Posts: 180
Re: Shoulder Design Discussion?

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 ]
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  #10  
Old 03-06-2002, 08:16 PM
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Join Date: Aug 2001
Location: Pa
Posts: 45
Re: Shoulder Design Discussion?

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
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  #11  
Old 03-09-2002, 12:24 AM
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Join Date: Mar 2002
Location: KY - LA
Posts: 40
Re: Shoulder Design Discussion?

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.
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