Hello everyone,

I have a few questions regarding cartridge design. For ease of reading I will just list them. If it matters at all, the rifle would be a Winchester 94.
(1.) What are the pros and cons to wall taper, and what is the max and min ratio.

(2.) How does shoulder profile affect back thrust?

(3.) What is the minimun neck length? does this vary depending on bullet type?

(4.) How does bore diameter affect pressure?

I am planning on building and &quot;improved&quot; in either 25-35, or 30-30, maybe 35/30-30 and wanted to get a better understanding of the physics and engineering behind the &quot;improvment&quot; <!--emo&:)--><img src="http://beartoothbullets.com/iB_html/non-cgi/emoticons/smile.gif" border="0" valign="absmiddle" alt=':)'><!--endemo-->
Thanks Much
Juan

Hello Juan!...I will attempt to answer your questions. Yuo are already on the right track, with the important factors to consider whether you are building a wildcat or selecting one.
1 The wall taper is very important especially in lever guns. The flater the wall taper the less back thrust to the bolt. Parker Ackley proved this. Besides increasing the powder capacity the reduced wall taper reduce case stretch. Two of the worst case designs for bolt thrust and strecth are the .348 Winchester and .280 Ross.
2. Shoulder profile is more important in powder burn and throat erosion than anything else. The flatter the wall taper and sharper the shoulder angle, the less the powder will be &quot;funneled&quot; into the front of the case as pressure rises. Some designers believe that there is a plug of powder blown into the barrel burning and the sides burn in the case. Another advantage of the sharps shoulders is, the angle that white hot powder particles intersect inside of the case, instead of the throat. This redues throar erosion.
3. The neck of the design should be long enough to cover all the lube grooves and base of hard cast bullets! If this is not done, no real accuracy will ever happen. On jacketed bullets the base should always be ahead or at the junction of the neck and shoulder. Ifnot, and is down in the powder, you have reduced powder capacity.
4. With all things being equal...case capacity, case shape, powder type and weight, bullet weight, and pressure..the larger base area of the bullet, since the gas has more area to work on, will be ay a higher velocity. Of course the shorter fatter bullet my not have as good a BC. Both wildcats you mentioned are excellent, but my nod would be to Ackley's .30-30 Improved.With it's reduced bolt thrust aand improved case capacity, it performs far beyond the standard .30-30. With its long neck, it is ideal for cast bullets.
I hope this answered some of your questions...Best Regards, James

(Edited by James Gates at 10:57 pm on Feb. 27, 2001)

James,

Thank you for the information! It seems my pseudo wildcat project has taken a turn, however a forward one. A wildcat that I had thought of earlier, but put on the back burner was a 35/30-30, or something similar.

Today I picked up an octagon barrel for my 94. I have not yet slugged the bore, but it is stamped 357 max (maximum?) Thge length is 20&quot;, and it is nickel steel, so pre-war? At any rate, I suspect it was a 25-35 or 30-30 barrel to begin with. I am guessing it was shortened at both ends, to provided the proper size to be able to cut a chamber for the 357 max. At any rate, it clocks up perfectly on my receiver, and the dove tails, are in great shape. With this comes more questions for you, so here we go again <!--emo&:)--><img src="http://beartoothbullets.com/iB_html/non-cgi/emoticons/smile.gif" border="0" valign="absmiddle" alt=':)'><!--endemo-->

1. Depending on the bore size, which I have not slugged, is it safe to interchange 357 pistol, and 358 rifle bullets, or are the .358 jacket bullets too tight in a .357 bore?

2. Have you ever played with, or read anything regarding a 35/30-30 or similar? I have also read about a 357 bullbery, which seems to be a &quot;ackley improved&quot; style 35/30-30. This is what I am really leaning toward if I can find more info on it.

3. Would you estimate case volume would be in the league of the 35 Remington?

4. Rate if twist min and max?

As before, thank you very much for your insight!

Adios
Juan

Juan...I'm at a loss on the barrel? It sounds like a rebore job to me. I think I would make cast of that chamber to find out just what it is. Some where in the back of my mind I seem to remember that the Mod 92 threads were the same as the Mod 94...I'd have to check that. Some one may have set it up for a 92. Be sure and check that since the rim is much smaller on the .357 Max than the .30-30. There would be a lot of trouble on the cartridge cutoff out of the mag tube on the 94.
As for the .35/.30-30. I have not work with that one so I'll pass to Marshall. I think he has worked with it. I do under stand it's a little hotter than the .35 Remington. Sorry I could not help more!
Best Regards, James

Juan, from your two above posts, I think P.O. Ackley's books 1 and 2, as well as &quot;Cartridges of the World&quot; are appropriate.

But on barrel bore diameter and pressure, I can calculate the stress on the steel in the barrel.
The thin wall hoop stress is directly devirable:
The inside diameter &nbsp;times the pressure is the force, and the thickness
of two walls are in tension, hence:
Steel stress R = [ID][P]/[[2][wall thickness]]
The stress to break off the barrel like a lizard's tail is:
Steel stess L = [ID][P]/[2][pi][wall thickness]
This is why pressure failed barrels always fail lengthwise and never radially.


To be correct for thick walls, I have to mention Lame.
When the walls are thin, Lame's Formula gives the same answer, but as
the walls get thicker, Lame's
formula gives an increasingly &nbsp;greater stress.

I got Lame's formula from &quot;Mechanics of Materials&quot; &nbsp;by Laurson and Cox,
1938 Wiley and Sons.
The derivation was first done the the French mathematician, Lame, 500
years ago. It is a difficult derivation.
If the barrel is thick, read an two inches further down my post to Lame's formula:



S=P(r2 squared +r1 squared)/(r2 squared - r1 squared)

Where S is the stress in psi of tension

P is the chamber pressure in psi

r1 is radius of the chamber or bore in inches

r2 is radius of the barrel [center to outside] in inches&quot;

Juan,

Before any modifications are done, you should thoroughly consider one question-

What do you want to do with this gun that can't be acheived with an existing cartridge?

Wildcats can be interesting, but if they were really an improvement some arms maker would've adopted them. After all, if they can't sell &quot;new and improved&quot; they're out of business. The only ones that made the cut, so to speak, were the .257 Roberts, 25-06 and .35 Whelen. Two of the three are barely alive today in a commercial sense, regardless of the fact they are excellent and useful rounds.

There really is nothing at all wrong with a standard .30-30 or .35 Remington. In fact with today's bullets, propellants, and stronger brass they are much better cartridges than when introduced.