How does shoulder angle/neck length affect a cartridge?

G

Ginner

Guest
Does anyone out there have any hard evidence as to how, for example, a 40degree/longneck combo would perform vs a 30degree/shortneck in respect to erosion and accuracy on an otherwise identical cartridge?
I'm asking this because it seems to me(rookie) that AI anything seems to be a better cartridge but most "bench" guns use shoulder angles "around" 30 degrees; is this just to make it feed more reliably? If a case is changed to a steeper shoulder with a longer neck would it not move the turbulance lower in the neck and give a more complete burn in the case resulting in a more efficient cartridge and less throat erosion or is my inexperience shining through here?:confused:
 
Ginner

Gene Beggs has developed his line of chamberings using the 220 Russian, right out of the box. The 6mm Beggs is just necked up, and the 220 Beggs is a 220 Rusian with a small radius at the neck shoulder junction. (I think that is the only difference).
Both retain the stock body taper, (pretty steep), and the stock shoulder angle, (pretty shallow). Sort of "anti-Benchrest".
By all accounts in his tunnel testing, the 220 and 6mm Beggs are just as accurate as their PPC counterparts........
The throat erosion thing. We don't worry too much about that......jackie
 
Does anyone out there have any hard evidence as to how, for example, a 40degree/longneck combo would perform vs a 30degree/shortneck in respect to erosion and accuracy on an otherwise identical cartridge?
Click to expand...
Not to be terribly rude, but if there were compelling evidence, we'd all be shooting the configuration that had proved "best." You see anecdotal evidence ("my . . ."), but then somebody pops up with just the opposite. We may not be the swiftest arrows in the quiver, but we would catch on after a while.
 
300 Savage uses a 30 deg shoulder same case length as .308 but has a shorter neck.

22-250 Savage has a 28 deg neck.

Ackley improved designs are 40 deg usually increase the case capacity of the cartridge.

30 deg in a 6ppc is for better consistancy and slightly larger capacity than a 220 Russian.

The steeper the shoulder angle the heavier the bolt thrust so most factory hunting cartridges use shallower shoulder angles for safety reasons as the tolerances are not up to precision standards in bench rest actions.
 
What are you basing this statement on DaRealViper???


quote >>> "The steeper the shoulder angle the heavier the bolt thrust" <<<


Care to elaborate?


al
 
DaRealViper said:
The steeper the shoulder angle the heavier the bolt thrust so most factory hunting cartridges use shallower shoulder angles for safety reasons as the tolerances are not up to precision standards in bench rest actions.
Click to expand...

Shallower shoulder angle gives more reliable feeding. Shallower body taper would yield less bolt thrust. P.O. Ackley used a 40 degree shoulder and shallower body taper to gain case capacity.

Other than adding case capacity, the 40 degree shoulder adds little. A steeper shoulder angle would add some to headspace accuracy, but with lots of neck tension retards seating depth accuracy. The steeper shoulder is easier to flex in bullet seating in a tight tensioned neck.
 
What is really going on

The PPC seems to be the stick in the mud. All of the "glossy covered" magazines base all of the "short and fat is better" theories on the fact that the 6PPC dominates 100-200 yrd Benchrest.
But, I would challenge anybody to assemble a 222 Remington with the same fine components as we use in the PPC, go out to Beggs' tunnel, and see which one is really "more accurate" as defined by a cases ability to stack one bullet on top of another.
Any bets on which would come out on top???.......jackie
 
so most factory hunting cartridges use shallower shoulder angles for safety reasons
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The old wives tale I believe in is the reason for lower-degree factory shoulder angles is simply because it is easier to make the cases, not any safety factor.

As for body taper & bolt thrust, I seem to remember that Ackley himself later remarked that greater body taper didn't "increase bolt thrust." All of this is a friction phenomina; the case walls "grabbing" the chamber. You're going to get the same friction with a tapered case as with a straight case, as long as the pressure curve is the same.
 
There is an actual example that you might be interested in (not directed at you, Charles E), the 22 Remington Jet. This is a rather tapered, and rounded shoulder cartridge that Smith & Wesson chambered in a revolver years ago. It was notorious for "jamming" the cylinder if it wasn't kept spotlessly clean of oil, whereas the so called "straight-wall" pistol rounds, even at similar pressure levels, did not show this tendency.

This may not PROVE that more tapered cases exhibit more "bolt thrust", but it sure makes one think ;). Yes, it is a friction based phenomenon, but it illustrates that the case does in fact have more of a tendency to move backward on firing if it is more tapered. Does this increase "bolt thrust", you be the judge.

http://www.buffaloarms.com/prodimg/AMO22REMJET.jpg

Jim
 
Discussion can't hurt.

I wasn't inferring that I was reinventing the wheel. I am certainly not smarter than Ackley, Palmisano, Beggs...etc. or even as smart as most people on this site; of that I am certain. I just don't know if the question has been asked and I would like to learn.
Has anyone ever done the AI thing to a 6BR? I'm just wondering what the effect would be if the shoulder was sharper and the neck kept as long as possible on a short fat cartridge. I would love to see if the (dare I say it), WSSM were a long necked AI with a small rifle primer. Would it be an accurate long range round or just an explosive device?:confused:
 
The cartridge case is rather thin and weak right ahead of the solid case head. I do not believe that friction ahead of that area has much influence on actual bolt thrust. Internal pressure against the solid case head dictates bolt thrust pressure. I think......
I'd like to hear what Jerry Stiller and some of the other degreed Engineers have to say on this topic. Or physics majors.
 
Jay,

It could be worthwhile to read Acley on the experiment he did with a 30/30 Ackley in a M94 lever gun without locking lugs. I'm surew that it would convince you that the cartridge case can & does absorb a significant percentage of the thrust from ignition.

John
 
alinwa said:
What are you basing this statement on DaRealViper???


quote >>> "The steeper the shoulder angle the heavier the bolt thrust" <<<


Care to elaborate?


al
Click to expand...

I wondered about that too...
 
jackie schmidt said:
Did Ackely remove the rear locking breech plate from that 94 action
Click to expand...

jackie,

The article's worth checking out. He reported that the primer backed out slightly but the case didn't move. It would be interesting to know what pressures he loaded to, considering that that the case absorbed the pressure spike, but the primer did act to a small degree on the breech block & backed out a tad. I calculated that a LR primer would have a tad over 1000 pounds of thrust at 30000 PSI & around 1400 at 40000. Hell, I used to hold more than that firing .22 ammo in my Stevens Favourite with the sloppy pin by pressing my thumb on the edge of the block.

In an extreme case, he backed the barrel out two full threads, lengthened the firing pin & fired the round, the result being the primer ejecting from the pocket & the case staying in the chamber, as it had when he backed it out one thread & in every previous example. In these cases, the locking system was intact.

P.O. Ackley Handbook for shooters & reloaders Volume 1 - Pressure

John
 
Questions? Lotsa questions.

Has anyone fired enough rounds through the 6BR-DX to compare with the 6BR for barrel life? Could 22BR brass be used to form a longer necked version of the 6BR-DX? Has anyone gone beyond a 40° shoulder to say a 45°?
 
Could 22BR brass be used to form a longer necked version of the 6BR-DX?
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The 22BR is formed by necking down 6BR brass. Very nice varmint round.

Tony
 
Tony, that's what I'm wondering; if you put a 22BR case in a 6BR-DX would the resulting case be a 6BR-DX but retaining the full length BR neck?
I have no experience fireforming so I don't know if it would work that way, overwork the brass, or just split the neck.
 
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