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Thread: case shape...again...

  1. #1

    Default case shape...again...

    My apologies to the dead horse, but I'm still curious about the recoil thing.
    A little while back we discussed internal ballistics a little bit, particularly the relation of case shape to the "Bill Lear effect", and in turn its relation to recoil. I think we concluded that two major factors that are difficult to really figure for are case length and shoulder angle. However, as was mentioned, short cases have to have sharp shoulders. The only way to avoid the shoulder is to lengthen the case and taper it like the H&H.
    So here's my question- since we have to choose between short case and no shoulder, which do you think is the bigger contributer to the "bill lear effect"? Could you knock off more of that jet effect by shortening the case and leaving a sharp shoulder, or by lengthening the case and just tapering it?
    Even though I've really liked the short-mag concept, I almost wonder if its purpose is defeated by the necessary shoulder, and if the longer case is worth it for the sake of achieving an H&H-like taper.

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    Default A wounded horse..

    I don't think he's dead yet.

    Your theory has merit but there's more to consider.

    To compare recoil between two case shapes we would first have to bring about two ballistically equal calibers with very different case shape. Because, certainly recoil of the 38 spcl is less than the 300 Win Mag, but they are not equal in Muzzle Energy. We may be able to produce the same ME with differing amounts of the same powder. That would be due to a more efficient design. Meaning the propellant would be better utilized, or burn more cleanly and more energy extracted from it. That would give less recoil because of less powder used.

    The Lear effect is a product of 1.) Exit pressure and 2.) Exit velocity.
    These numbers are affected by the quantity of powder that burns and the rate at which it burns. With larger capacity cases lots of powder is unburned and it produces X fps. With more compact cases, about the same amount of powder is burned (but less was loaded) and still can produce X fps.

    This efficiency of powder burn is also affected by the shape of the case. Long shallow tapered cases are not efficient with smokeless powder. (But are better for black powder.) The reason for this is that the powder column is launched by the initial ignition and burns as it moves on it's way down the barrel. (This happens quickly but still happens.) With a short compact powder column of the same volume, a greater velocity and therefore ME figure can be had because more of the powder is burned, due to larger area of powder exposed to the initial ignition.

    A very good case study (pun intended) would be the 300 WSM and the 300 H&H. The have very similar case volume and very close ME figures. Grain for grain the WSM will out perform it. But this margin is so small that it would be hard to detect because it would be masked by the normal variations from one rifle to the next. It would take a very close match between barrels and chamber tollerances to show this advantage.

    Another point here is the larger the bore the more efficiently the powder is utilized and this is the obvious factor when we start testing on the same case. Case in Point; (pun intended) the 270 WSM vs the 416 WSM. Same powder charge much more energy from the 416. (Yes I know the burn rate differs greatly.)

    Your long shallow tapered case will definately produce less recoil than the same volume short fat case, of the same caliber. But the reason is that the ballistics, the muzzle energy produced, will be less than the short fat case, due to the inefficiency of the design. The powder doesn't burn well in th elong tapered case.

    Now don't take this to mean that the old 300 H&H is a slob and can't get out of it's own smoke. I am not saying that at all, it is not a bad caliber. We are splitting hairs here and it's hairs are thinner. The hype behind the WSM calibers is/was about this more efficient design. Technically it "produces the same ballistics with less recoil" simple due to this paper thin theoretcal advantage. On the shoulder we can't tell the difference. Until they make a 6 pound 300 mag, then it becomes obvious who kicks who's butt.
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  3. #3
    Moderator Paul H's Avatar
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    Default

    I can't say that case shape has no effect on recoil, but I would bank on it being in the marginal category.

    Personally I look at what I bullet I want to launch at what speed, and that will require a certain amount of powder. Then I look at suitable cases. Then I look at what type of rifle I want, I short action, std action, long action.

    Dealing with recoil is a factor of rifle weight and stock design.

    I believe John Barsness did a fairly thorough comparison of the 300 WSM and 300 H&H and his results are the two rounds are a wash performance wise. The 300 H&H has milder recoil because a mag length action is heavier.

  4. #4

    Default Rebuilding the Wheel

    Short fat cases aren't anything new. In 1974 when Ferris Pindell designed the 22 PPC He changed the shooting world forever. Nope, you guys don't really care about a 22 caliber bench rest cartridge. BUT, it's research is the basis of all modern WSM and SAUM cartridges. His research was the forerunner of all modern short, fat and efficeint hunting rounds. Until that time the height to width ratio was more like the 30-06 and 300 H&H shapes; Even belted magnums used about the same ratios. The exceptions being the 6.5 REM.MAg., 284 WIN, 350 REM Mag. all nearly dead or dying in 1974.
    A short fat case allows a larger volume of powder to ignite, thus reducing the amount of powder which is thrust into the projectile, a plug. It allows the pressure build more rapidly than a long slendor case of the same volume. A fat case with a minimum taper reduces bolt thrust; A case that is very tapered is like a splitting wedge as the pressure swells it to the chamber it is thrust rearward. This was realized by P.O. Ackley and Gibbs eons ago and is still true today.
    The only advantage of the modern WSM and SAUM type cartridges are there ability to be used in short actions, since most of these type cartridges use very close to there long action rivals quanity of powder and bullet weight. With the use of shorter ammo can come shorter rifles, but make them lighter and Einstein's law of Relativaty comes into play; For every action there is a reaction. A bullet launched at a given velocity takes a given amount of thrust (hot gas), in an equal enviornment it produces a given number of foots pounds of recoil.

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    Default Wave Structure of Matter (WSM)

    Quote Originally Posted by brav01 View Post
    Short fat cases aren't anything new. In 1974 when Ferris Pindell designed the 22 PPC He changed the shooting world forever. Nope, you guys don't really care about a 22 caliber bench rest cartridge. BUT, it's research is the basis of all modern WSM and SAUM cartridges. His research was the forerunner of all modern short, fat and efficeint hunting rounds. Until that time the height to width ratio was more like the 30-06 and 300 H&H shapes; Even belted magnums used about the same ratios. The exceptions being the 6.5 REM.MAg., 284 WIN, 350 REM Mag. all nearly dead or dying in 1974.
    A short fat case allows a larger volume of powder to ignite, thus reducing the amount of powder which is thrust into the projectile, a plug. It allows the pressure build more rapidly than a long slendor case of the same volume. A fat case with a minimum taper reduces bolt thrust; A case that is very tapered is like a splitting wedge as the pressure swells it to the chamber it is thrust rearward. This was realized by P.O. Ackley and Gibbs eons ago and is still true today.
    The only advantage of the modern WSM and SAUM type cartridges are there ability to be used in short actions, since most of these type cartridges use very close to there long action rivals quanity of powder and bullet weight. With the use of shorter ammo can come shorter rifles, but make them lighter and Einstein's law of Relativaty comes into play; For every action there is a reaction. A bullet launched at a given velocity takes a given amount of thrust (hot gas), in an equal enviornment it produces a given number of foots pounds of recoil.
    Well, I didn't say I invented them. I'll leave credit for them to Pindell and Palmissano and Rick Jamison, more recently. Keeping in mind the case dimensions of the PPC's were established in Russia in 1943.

    You contradict yourself here about the advantages of the short fat cases but I let that stand.

    What I do find a bit out in left field is your assignment of Newton principles to Einstein and mention his Metaphysics of Relativity to describe recoil.

    Einstein's Theory of Relativity and the Wave Structure of Matter (WSM) (Thats funny, huh? ) has nothing to do with recoil.

    Newton's Laws of Physics.

    1. Law of Inertia- (Mass in motion) Objects in motion tend to remain in motion in a straight line until altered by some external force or field.

    2. Law of Force-Force (F) is equal to mass (m) * acceleration (a). Note this is acceleration, a vector sum, not velocity as earlier thinkers believed.

    3. For every action there is an equal and opposite reactions. This is the principle that gives us recoill. Sometimes called the law of equal momentum.

    In 1687 Newton did write a great deal on what Einstein is credited for and that is his theory of Time and Particles of Force and his Time-Motion Theory. But I don't think Einstein cared much for the simplier laws of Physics.
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    Default

    Gentlemen:
    Check out John Barsness’ short article on “Case Shape” in the latest Handloader Magazine.

    A rifle was first chambered in 300 H&H, then in 300 WSM. The barrel lengths and case capacities, were essentially the same, as were the seating lengths the loads, etc. Practically speaking, only the case shape was different. Very different.

    Velocities, pressures, and accuracy results were also essentially the same. JB’s closing statement,,,,

    “Again, this was a limited test, but in this instance (an example of one), it appears that case shape doesn’t make much difference.”

    One can theorize until the cows come home, but here is a test that IMO, has validity.

    Of course I would like it, because it confirms my own speculation that case shape has little to do with anything ballistically. Surely, the advantages or disadvantages of one case compared to another is only in how it effects the case itself, or how suitable the case is, for a particular application.

    Smitty (Speculator) of the North

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    Default Einstein couldn't balance a checkbook?

    I like short, fat cases. They resemble me! Plus, the cases don't stretch a lot, and being a lazy type who absolutely detests trimming and chamfering cases, short fat, non-stretching cases are GOOD.
    By and large, they shoot pretty well, too.
    Being lazy, or at least not inclined to expend more energy than is necessary to get something accomplished, using something like a short actioned .284 Winchester to get the same performance as a .280 Remington, and not having to pull and push that bolt as far is a plus.
    Time saved in not performing unnecessary functions gives more time for other activities...
    Oh, I was always under the impression that a certain volume of gas combined with bullet weight will pretty much deliver the same amount of 'equal and opposite', whether it comes from short fat, or long skinny, as long as the velocity of that exiting gas and bullet are the same. Or do I need more exercise?

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    Default

    What is a "Bill Lear Effect"? Is this anything to do with a Lear Jet? Like the kind you fly to another city in?

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    New member George's Avatar
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    Default Lear

    Actually a term coined by or at least used here on the Forum by "Murphy" the moderator. Has to do with the portion of firearm recoil produced by gas escaping out of the muzzle after the bullet leaves. The concept is more akin to a rocket motor than a jet engine (as in Learjet) but the ideas are similar. That type of propulsion has been used since the Chinese or earlier? first used burning powder to propel fireworks.

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    Default

    I see. Well to calculate the overall recoil of the rifle this is included, and it is the weight of the powder gases (use the weight of the solid powder), moving about 5200 fps.

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    New member George's Avatar
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    Default recoil calculation

    Well, kinda I guess. Including muzzle velocity of the bullet, the weight of bullet plus the weight of the powder and the weight of the rifle then using the "equal and opposite" equation(s)... the recoil energy and recoil velocity can be calculated. Those are the numbers generated on the numerous recoil calculators found on the internet and in ballistic software programs. BUT, describing and quantitatively including the rocket thrust effect in addition to the simple bullet + powder acceleration is more complex. Enough so that it may be easier to mount rifle (x) shooting ammo (y) on a dynamometer, firing the gun then looking at the true parameters of recoil as recorded by the dynamometer. A while back a lengthy thread covered a bunch of this stuff... that's why go_north was talking about 'dead horses'

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    Default Gas Kick...

    Quote Originally Posted by Nitroman View Post
    I see. Well to calculate the overall recoil of the rifle this is included, and it is the weight of the powder gases (use the weight of the solid powder), moving about 5200 fps.
    Nitro,

    Just curious, where you got the 5200 fps number? I have seen and used 4400-4800 fps for the exit velocity of the gases but not seen 5200.
    Here is a link to my formula for the recoil equation. Try it sometime. It does use some rounding and mean constants, but is a good approximation. Enjoy.


    http://forums.outdoorsdirectory.com/...ead.php?t=7603
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    From Any Shot You Want by Art Alphin.

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    Default Thanks,

    Quote Originally Posted by Nitroman View Post
    From Any Shot You Want by Art Alphin.
    I have that book, that loading manual and enjoy it a lot. I didn't know that was in there. I'll have to look at that tonite.

    He was an instructor of mine for a short course I took at Monterey some many years ago. He has always been his same charming self all these years.

    I get to visit with him at he SHOT show and Safari Club sometimes. He is no longer running his company but is still on as a "consultant". Smart guy, no doubt, and that "Any Shot You Want" is a great book and very readable. I have learned a lot from it.
    Is there nothing so sacred on this earth that you aren't willing to kill or die for?



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