Shoulder Angles--lets get technical!

[Cybra]

I am one of those people cursed with few ambitions and delights in life; studying interior ballistics happens to be one of those aforementioned "fews". I've heard a lot of controversy over various case designs <of course>, and I'm minutely aware of some very interesting experiments ongoing as I type this. Now, stickly regarding conical shoulder configurations, as that's what I'm stuck with more-or-less for reasons of economy and practicality, I would utterly love to hear some comments. For example, I have heard that the best compromise to achieving what a hemizoidal <spelling??> shoulder will accomplish is a 30 degree shoulder. Humorously, though, I have also heard comments, supposedly from similar and, on occasion, same sources indicating that efficiency with a 45 degree shoulder is best, if the hemizoid cannot be used. I am familiar with the "well, it works for me" attitude--fair enough. But we all like to dream, and question, and I truly enjoy reading what others on this site have to say [thus far, it's the most educational single-source site I have come to.]

So here we go--concerning shoulder angles between 30 and 60 degrees, what are some thoughts? I'll list my intentions as this: take a 6PPC case, push the neck-shoulder junction back until a 45 degree angle is reached, leave the neck long <.3488", approx.>, and try some of Bounty Hunter's last link-listed tactics. I am familiar with that approach, and it sounds very mathmatical and swift. BUT--before we build this freakish thing, I'd like some consultation with the champs...

Anyone who feels inclined to share some tidbits, please do so--it will be very much appreciated, and should we bump into each other at an Irish Pub...well, first round's on me.

Dave

 

[Mysticplayer]

What are you trying to achieve with these shoulder angles? How about case taper?

Jerry

 

[dbhostler]

Maybe a book by Dr. Ken Howell can help in your design. The name is "Designing & Forming Custom Cartridges", it's available online from www.sinclairintl.com.
db

 

[Cybra]

Hello, Jerry

What am I trying to achieve? I would like to see how fast I can waste a couple `grand.

No, seriously, here's the scoop--6PPC case will be shooting Berger's 95gr VLDs. As such, I plan on running slow powders, and the sharp shoulder configuration should help with combustion. Case taper will be the same as a standard PPC [.4402-.4310 I believe are the specs]. The only things I'm considering changing are the shoulder angle and neck lengths; I want to push the shoulder back about .0650 or something in that arena, and leave the neck long. I have heard some comments about barrel shock waves forming with sharper shoulder configurations; I have also heard combustion effieciency is improved--to a point. In short, I've heard a lot; I was just hoping I could hear from some of you fellas as well. <hands up> Just a little puzzle!

DB I am familiar with the book. I'd love to get it, in fact, but cash is not plentiful for this college boy.

I figure the worst that can happen is I'll build a $5000 gun that won't shoot for ****.

But hey, life's a trip, right? I'd just prefer not to model it after Trains, Planes, and Automobiles...

Dave

 

[dbhostler]

Some time ago, a local smith was telling me about a new cartridge that had been developed that was blowing the doors off the PPC. As usual I have forgotten the details, but it was something like a shortened 250 with a long neck in 6mm. I think this was in the benchrest circles. So you may have something with the long neck idea.
db

 

[BountyHunter]

Think he is talking about the variations of the 250 case the highpower shooters are using along those lines. You can go to long range target shooting.com and read the threads. However, they only build guns and chambers to high power accuracy levels of .5 moa. For example almost non are tight neck and cases are not neck turned etc. Most LR BR 1000 yd guns are down in the .1-.3 moa minimum. Just a rule of thumb I have used, take the average group at 100 say .2 multiple by 10 (2 inches)and double which would be about 4 inches at 1000. Now that leaves not fudge for wind and operator headspacing. But if you look at what most LR guns do at 100 and then compare to 1000. That will put you pretty close.

 

[Cybra]

Hello, Gentlemen!

Again, I thank you for responding, and the addition of some follow-ups. If I had to take a guess on the variation a couple of you are mentioning, it would be something similar to a 6mm Dasher case [I think it's a 250 case midified in a shorted 250 die?] I have heard something of a shortened 6mm BR case as well, I think it's called the Tall Dog? I think the dasher case operates with either a 35 or 40 degree shoulder, but I'm not positive.

DB My specific reasoning for the long neck was this; with a sharp case neck such as I was thinking, the powder-gas has the tendency, from what I've heard, to want to "spray" out of the case in a more pronounced conical direction, and the sharper the shoulder and shorter the case neck, the more magnified this event becomes. I have no way of knowing, but it SOUNDS reasonable. So the longer neck may help in initial directioning of the powder-gas, and might help minutely in throat wear and blow-by--maybe.

Damned if I know, I'm just a redneck!

Bounty Hunter, again I thank you. I will indeed check that post out. Seems there are quite a few good ones out there that I've yet to hear of. Gives me something to keep me sane until I get back to God's Country...

John, that is a darned good idea--he would be a likely fellow to ask! I will see if I can drop him a note, and relay back what he says just for some good ol` reading. I will also wish him well on everyone's behalf here. Thanks for the lead. I suspect this project could get very interesting. I know one thing; cartridge development over the last ten years [last five to really get into the heat] has been extremely intriguing. Again, thank you all for replying, and everyone have a happy, fun, and fattening holiday [the fatter y`all get, the slower you move, which means I might be able to beat a couple of you to the few remaining Heavens of Hunting.]

Dave

 

[Guest]

Hi,
You might want to ask Dr. Howell hisself.
I think that he usually hides out on the 24hourcampfire.com board.
His health hasn't been to good, lately, so it may take a few days to get a response. Tell him we all said "Hi" from here. And, we miss his posts.

Merry X-mas.
C'ya. John.