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Shoulder Design Discussion?

 
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  #1  
Old 03-05-2002, 02:21 PM
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Join Date: Mar 2002
Location: KY - LA
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Shoulder Design Discussion?

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? [img]images/icons/confused.gif[/img]

Thanks for the info.
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  #2  
Old 03-05-2002, 02:31 PM
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Join Date: Jan 2002
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Re: Shoulder Design Discussion?

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 [img]images/icons/tongue.gif[/img]

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

Peter
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  #3  
Old 03-05-2002, 04:26 PM
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Location: Stevensville, Montana
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Re: Shoulder Design Discussion?

"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 ]
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Old 03-05-2002, 05:52 PM
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Re: Shoulder Design Discussion?

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.
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  #5  
Old 03-06-2002, 07:08 AM
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Re: Shoulder Design Discussion?

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
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  #6  
Old 03-06-2002, 08:17 AM
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Re: Shoulder Design Discussion?

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
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  #7  
Old 03-06-2002, 08:48 AM
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Re: Shoulder Design Discussion?

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
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