Home Forums Hunting & Shooting Ask The Gunwriters Cartridge Efficiency: Why case shape matters

I suspect this cartridge epiphany is along the lines of "cold fusion." In the end, any gains in efficiency will be found to have been experimental error.

I had QuickLoad pretend the gases didn't accelerate at all, they just magically push the bullet without having to accelerate themselves. I also shortened the case to pick a little extra expansion ratio. Even in this land of make-belive, efficiency was raised only 14%, less than claimed on their web site.

In looking over the web site and the US patent, I don't see any experimental evidence backing up their claim. The tests at Norma didn't even use the same primer in the two cases compared!

To be sure, coating the cases and bullet with heat insulating material must up efficiency some. The mysterious focusing of the primer shock is certainly an interesting theory, but where's the data backing it all up? Some of their claims for efficiency are based on an assumption of powder burning I don't believe has been demonstrated.

As always, the proof will be in the pudding, and that doesn't appear to even have been cooked yet.

Personally, I don't care it Z-Hat's cartridges are technically the most efficient rounds on Planet Earth, and live up to the claims of their originator. There's more to cartridge selection than all that nickle & dime stuff.

The one thing I know is, Z-Hat's cartridges present some real logistical problems that, in a very real way, make them inefficient by default.

Not for me..........

AD

AD, How right your are! My buddy has had a set of dies on order from Zeglin for over a year now, and still hasn't even been promised a delivery time. Maybe there are some issues involved.....................DJ

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All righty then.

The shouders would, will and do hold more of the unburned powder from being pushed up the barrel. In doing so it exposes more powder to the flash (according to page 23).

Which one will hold back a more predictable and consistent amount of powder? A short fat case or a long thin case.

It looks to me as though a long thin case would exposes a greater surface area to the flash in a shorter amount of time once the "plug" moves but with the same percentage of deviation in plug size the short fat cartridge would be more consistent in the amount of powder being exposed once the "plug" moves.

This would mean that the case would have to be proportioned to each cal. Such as the .30-06 to the .50BMG. No famly of cartridges like .308, 7mm-08 and .243.

What would a .30 cal. look like if it had the proporition of the .243WSSM???? What would the action look like? Could the old school deal with it?

If a new cartridge design is to be more efficient at converting powder energy to bullet kinetic energy, then it has to reduce one or more of the known causes of energy loss:

1. When the bullet leaves the muzzle, the propellant gas vents into the air. Compressed gas has potential energy, so venting it is a loss of energy. In the case I have calculated, it carries away more energy than the bullet. (Relates to 2525's statements about peak pressure and expansion ratio.)

2. Friction robs energy. It's not much, roughly 300 foot pounds.

3. Hot gasses are in contact with steel, and the steel absorbs heat. This is a big source of energy loss... probably about 1,500-2,000 foot pounds.

4. Rifle recoil carries away about 25 foot pounds.

So my question is, which of these is affected by cartridge shape? So far, I can't see where it has any effect on any of the known energy losses.

Mark me as deeply skeptical on that one.

OTH, I have handled a rifle with the new chambering, and the explanation I got of its benefit was quite different. The curved shoulder acts a focusing device, like a telescope mirror, to focus energy from the primer "bang" on a point near the front of the cartridge, giving "dual ignition" and better burn consistency. Now that sounds plausible.

Are we looking for "known causes of enery loss" or ways to be more efficient in energy generation/conversion?

280don

The March/April 2006 of Rifle Shooter magazine has an article by M. L. McPherson alleging case shape matters. It is 3 pages long with several diagrams, internal and external, explaining the position.

Do you think the curved shoulder acts as a focusing device once all the powder has burned to expose the curved shoulder? I know that the artical shows this.

I think the Vee or cone shape of the unburned powder behind the shoulder would have this effect.

I'm not a good person to take on this one. My pet deer rifle is an A-Bolt S/S in .25WSSM with a 120gr bullet. The rifle just feels right in my hands. What I think is more important is staying away from sound barriers. I can live with less then MOA and some flattend primers.

I also like the .22Hornet. It's in my speed zone. The .22Hornet case shape and shoulders couldn't be more different then those of the .25WSSM. My CZ 527 and A-Bolt are the same size! So you can see what is important to me.

Anybody remember who the "experts" were who were shooting for the 5000Fps mark. Last I heard from several years ago, they had given up due to impractical barrel length, and unforeseen problems with projectiles and other components.

Think they were involved with some kind of military research, but were also looking for a "zero gravity/friction/hyper" varmint round with possible commercial applications.

I think they did have some success with the high 4000fps.

Front venturi burn effect is not new. Method to achieve might be. Elmer Keith and two partners formed a rifle company some time back and went broke. From what I read there was some merit to what they were trying to do, and also a awful lot of pro and con debate over their idea.

They called their rifles and cartridges OKH (K for Keith), and don't remember the names of the other guys. I think Bob Hagel used some of these rifles quite a bit until the split.

Doggone it MColeman! If your quote from Jeff Cooper is accurate, I just found out I've got an inferior mind.

However will admit: A good idea is interesting, and I did buy a 17M2 because the cartridges were too cute to resist. And, I do think eventually we will probably see the M2 go the way of the 5mm rimfire.

Anything there redeem me somewhat?

P.S. I keep waiting to see some guy walking down the street in the city wearing the M2 as earrings. AND, IT AIN'T GOING TO BE ME!

O'Neil and Hopkins were the other two.

Deersmeller,

Thank you sir!

I have Elmer Keith's old .285OKH Mauser, the rifle on which he did the front ignition flash tube development and which is photoed in his books, plus 18 of his loads with flash tube, 55 grains of 4350 and the 180 grain WTCW bullet. Some year if I live long enough I will shoot some over a chronograph (which if EK did he never wrote about in print) and we will see how fast it is.

Come up to CT! I have a Oehler with a 4' three trap bar and it gives reliable readings.

PM me and we can get together any nice day. The range is just off of I-84 east of Waterbury. It can't take more than 90 minutes from the city.

[color:"red"] [/color] I would like to suggest an internet search for the name of M. L. McPherson. I knew the name, but my ole' mind could not place it. [color:"red"] [/color] I did and he has written for many years. Check your copy of Cartridges of the World. He and and Frank Barnes edited it. Mr. McPherson is well known and respected in the gunwriting community.

What he writes about in articles and books is well researched. Sometimes it gets a bit deep and is technical. However, I for one have read numerous of his pieces and have found no fault with his opinion.

I do believe I am correct, although not positive, it was McPherson's idea behind what we now know as "short Magnums."

Do not sell him short.

I think the reason the .30 hasn't been made is the bolt face diameter is to large and it would require a whole new action. 1 in the chamber and one in the magazine. This could be a problem.

No, sorry 280don. I was replying to MuskegMan's post, but just typed it in the quick reply box...

Should you ever get around to shooting and checking out your OKH, post your findings here for us if you will.

Will see what I can find in my library on them, though those books and articles have a tendency to "disappear" from my possession.

The best my memory serves me (about a 2 on a 1 to 10 scale): they did have some success with it in the field, it seems to me they had a problem with the venturi "burning out"; the venturi being difficult to "make", the venturi give "differing" results in test guns, the venturi was expensive to make due to the difficulty and probably not market friendly. Also I seem to remember EK having his "favorite" due to the bullet "failure issue", and seem to remember it was a .333 OKH and that he carried for several years on his pack-in hunts. The .333 (if right) being a favorite because of the bullets working like he wanted them too.

There are probably some other guys here with better memory than mine on this. Maybe they will chime in with some info.

Anyway you go, you've got a "one of a kind" there, and congratulations on your ownership!