Is there a resource available that can point me in the right direction to be able to calculate the changes different shoulder angles will present if changed? I am looking to answer some of the questions I have regarding this. I know a sharper or greater shoulder angle will produce more pressure, would just like to be able to predict it a little better and get a better understanding of the areas that are really affected. Any help would be appreciated.

Thanks in advance,

I would not really say more pressure, but perhaps a more efficient burn of the powder. Maybe one of the ballestic experts will chime in?

Three or so years ago maybe more, Precision Shooting had an article on predecting the ultimate shoulder angle. We tried out the calculations and came up with a 33.19 degree shoulder for a 300 Dakota and had a tight neck reamer ground. Did it work better? Can't really say.

Dave Kiff, Pacific Tool, the reamer maker, has a line of cartridges using a 37 degree shoulder, he calls them the "Rogue Cartridges". I have several of the Rogue reamers in the shop in the big 300's and a couple of big 338's.

Ackley's 40 degree shoulder is a little too much in some cartridges for good feeding.

So, it depends on just what your cartridge will be used for. In a single shot match rifle, up to 40 degrees is OK, and I have seen one 338 on the Rigby case with a 60 degree shoulder. Hunting rifles, magazine fed, should stay at 30 degrees or less for good feeding.

The only real way to find out exactly what is happening is to use a pressure test barrel, have a reamer ground, chamber up a barrel and run pressure & velocity tests. Then have another reamer ground and continue testing. And then you are at the mercy of barrel variations, unless you stay with the same barrel and rechamber. Even staying with the same barrel, you will have to start with the shorter shoulder cartridge first, then rechamber to the sharper shoulder, and you still will be at the mercy of throat erosion and wear of the lands & grooves near the chamber.

[ 05-20-2003, 02:05: Message edited by: John Ricks ]

mbmco,

It would be a good idea to try and find that reference JR noted. Actually I think it was a little earlier than 3 or so years ago that it was in Precision Shooting magazine. Unfortunately I haven't kept back issues of the magazine as I would like to refresh my memory about the article too. I'd guess it was about 5 years ago.

The reason I make this suggestion is that it was an excellent article and had to dowith "achieving turbulet flow" in the neck area. I believe the title had reference to that terminology. Apparently the combination of shoulder angle and neck length are critical because the shoulder angle determines where turbulet flow is achieved. If the shoulder is steep enough to have turbulent flow inside the neck, the throat erosion is significantly reduced. My recolection is that the optimum shoulder angle is near 30 deg so long as the neck is the right length. The 6 mm PPC is near the optimum combination and the 220 Swift is about the worst. And the history of barrel life certainly bears that out.

You might be able to get a copy of the paper by getting in touch with the editor of Precision Shooting magazine.

Good luck,

Don Shearer

JR & Don,

Thank you both for the suggestion. I will look for the article and if I get it I will share it with you. I am trying some different things out and just like to see potential problems prior to reacting to them. I will also bounce the ideas off of a ballistic friend too.

Thanks again,

I seem to recall a PS article in which Mic McPherson studied various shoulder angles (and shapes). I think he was trying to concentrate (or "focus") the primer's blast on the powder column just behind/under the base of the bullet, to get optimum burn/ignition of the powder column. They had come to the conclusion that an "eliptical" shoulder was best (tangent on the body, almost a right angle at the neck), and that concentrated the primer blast like a flashlight reflector focuses a light beam. This article was not that old - probably in the last six months or so?

I'll try to look for it and post if I find it.

Regards, Bill

http://www.angelfire.com/ma/ZERMEL/twist2.html

It's not terribly well written, but it does give you a summary of the turbulence point argument from PS. The argument is essentially that if you complete the truncated shoulder cone, then the apex of the cone should lie at a point distant from the plane of the case mouth by about 26.4% of the neck axial length. The expanding gases are presumed to follow the angle of the shoulder and to collide at this "turbulence point." That's a bit of a naive assumption about the gas dynamics, but it is probably reasonably accurate for relatively shallow shoulder angles. Keeping the turbulence point within the neck is supposed to reduce throat erosion, but the argument doesn't really say much about efficiency or accuracy of the cartridge... other than to assume that a turbulence point at the same relative distance as that of a 6mm PPC will produce performance similar to that of the PPC -- a rather large assumption.

Thanks I/S, I have had this idea for awhile now and have built some test bbls for it. I read this link a couple months ago, from when it was posted previously. Correlates what Don was stating too.

Bill, I will search for this article also. Will post how I make out with this.

Thanks again,

The disquisition on elliptical shoulders above reminded me of the 7mm Express cartridge. The design was by Roy Gradle, and I checked Ackley for the details. The case is the .348 Win (.300 WSM's parent case) with rim turned off, extractor groove cut and radiused shoulder shape formed in a hydraulic machine. The design is over 50 years old, but it is indeed short, fat and has an ellipical shoulder (since the circle is a special case of the ellipse).

For some years the idea of venturi-shaped shoulders was pursued by numerous wildcatters. It is nice to see the theory coming around again.

jim dodd

Don Shearer,

What is there about the shape of the Swifts shoulder that makes it different than say the .308 Winchester, 243 Winchester or the 257 Roberts?

It has been proven by actual testing over the past 50 years or so that case shoulder shape/angle has no significant effect at all on internal ballistics of two cartridges with the exact same CASE CAPACITY, CALIBER, and bullet weight! Short, fat cases do seem to burn powder more efficiently, and consequently produce more uniform velocities/accuracy, but this is due to the powder granules being closer to the primer, not shoulder angle!!

If you have a long tapered case with long sloping shoulder (such as the .300 H&H), and a short, minimun tapered case with sharp shoulder, like the .308 Norma, both of the same case capacity, and use the same powder type, same charge weight, and the same bullet in a barrel of the same length, the muzzle velocities of these two will not vary any more than from one rifle to the next using the SAME cartridge!

There was once a line of cartridges called the PMVF (Powell-Miller-Venturi-Freebore) which had a venturified shoulder/neck configuration that was just backward from that now found on Weatherby cartridges. Roy took the PMVF design, and reversed the venturi shape, but retained the freebore!! His cartridges essentially mimicked the PMVF rounds in ballistic performance. It was found that the improved MV of these two cartridge lines was due to the use of the freebore, not the shoulder/neck shape! The reason why Weatherbys won out?? Roy was a better salesman!!

[ 05-21-2003, 21:47: Message edited by: eldeguello ]

Sav99,

What is it? I'll have to rely on memory from the article (which I read some 5 years ago) about where the turbulence point occurs, to come up with an answer. What I recall is that the shallow shoulder angle along with the relatively short neck lead to the turbulence point being forward of the case and into the throat area. This caused erosion in the throat area. However, as you point out, the 308, 243 and 257 Roberts have quite similar shoulder/neck dimensions, so there must be something in addition to that. It has however been pretty well established that 220 Swifts do experience relatively short barrel life even as compared to the 308, 243 and 257 Roberts.

I'm afraid memory doesn't allow any more detail than that.

Don Shearer

I still remember Bob Wallack who was a gun writer in the 50's. Bob made a living out of bashing the Swift. I am still thinking of how he influnced me in 1957 to go with the 243 and not the Swift in the new M 70 Varmint rifle that I ordered. While both are a right answer I wanted the Swift but ordered the 243.

An argument could be made that the barrel life of these two cartridges is similar. If you would I compared the bore area to each cartridges case capacity. They are the same within 4%!

I used 48 grains of water for the Swift and 54 for the 243.

eldeguello,

Now my memory is being strained but I think that Weatherby used the PMVF design with their consent and that Huttons Rifle Ranch is where the testing was done.

On shoulder angles I am leaning towards the idea that there is a certain range for better combustion.

V.2 of Ackley has a lengthy write-up on the PMVF theory in the section on the PMVF Swift pp 135-136. P.O. writes that Weatherby used the PMVF style radius and a second radius at the shoulder.

jim

I know what you mean but it's not the expansion ratio which factors the barrel length and therefore has nothing to do with throat erosion.

As you recalculated the bore area vrs the case capacities we are in agreement really on the other points.

The comparison intends to show that there other cartridges with similar case capacities to bore area. To single out the Swift as a barrel burner perpetuates what I think is just a myth. Of course the Swift will eat up barrels but so will other rounds. As far as shoulder angles and neck length goes the advantage goes the the Swift vrs the 243 if indeed there is anything to the theory in the first place.

Most don't know that the Swift has as sharp a shoulder as some other popular cartridges.

[ 05-24-2003, 01:20: Message edited by: Savage99 ]

Interesting discussion. Have to put in my 2 pence on .220 Swift life.

For many years I shot a Pre-64 Win M-70 target, which came originally with two bbls., one installed, one waiting to be installed when the first burnt out.

When I sold the rifle in 1981 to Erv Heiman of Custom Gun Shop in Edmonton (he now owns Western Gun Parts), the second barrel had still never been put on. Of course, the first barrel only had something between 3,000 & 6,000 rounds through it, so maybe it was just getting well broken in (G). I used it mainly for crow shooting in Saskatchewan.

I suspect most .220 Swift barrels are not burnt out, but improperly and inadequately cleaned. About 5 years ago I bought a M70 pre-war standard weight .220 Swift. The bore looked pretty wretched, so I got the rifle for about $600. After liberal doses of Sweets and other goop, the bore looked pretty much pristine.

Then at the Portland gun show I managed to buy 20 boxes of Norma .220 Swift 50-grain loaded ammo for $100. Tried it in that Swift, and it would shoot 1/2" with that Norma ammo. Didn't try many different handloads with it for the first couple of years. Mine wouldn't shoot any better than that Norma factory stuff. Wish I could havve gotten 100 boxes of that stuff!

Obviously, that bore wasn't shot out either, though I don't know under what conditions of servitude it had labored.

Anyway, I have owned somewhere over a dozen Swifts, and currently still have two...a dogleg (flatbolt) Ruger M77 and a Riedl single shot. Both shoot fine and I stoke the coal to them.

AC

[ 06-03-2003, 02:38: Message edited by: Alberta Canuck ]