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Shell Velocity

Discussion in 'Shooting Related Threads' started by phirel, Nov 14, 2009.

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  1. phirel

    phirel TS Member

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    Why does the velocity vary +-30 ft/sec in a box of identical hulls loaded with exactly the same components?

    Pat Ireland
     
  2. hmb

    hmb Well-Known Member

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    The shells all have the same velocity, it's the cronograph that's screwed up. HMB
     
  3. Post  2

    Post 2 TS Member

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    HMB, what could you possibly base that assumption on? Post-2
     
  4. hmb

    hmb Well-Known Member

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    Devine guidance. HMB
     
  5. School Teacher

    School Teacher Well-Known Member

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    Pat:

    The logical answer is that the hulls, components and loading processes are not "identical". There is, I am sure, some allowable level of tolerance in the various manufacturing and assembly processes.

    Even you have remarked that the trees that Alliant uses to produce cellulose are not all "exactly" the same.

    How many things in life are "exactly" identical? Are all hydrogen atoms "exactly" the same? Does every electron have "exactly" the same negative charge.

    I remember reading years ago about one of the top shooters obtaining all of his ammo from a specific Remington loading machine. This was in Shotgun Sports as I recall and the article included a picture of the top shooter standing next to the machine.

    Ed Ward
     
  6. rick979

    rick979 Active Member

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    Do new shells from the same box chronograph exactly the same? I doubt it. Does the barrel temperature never vary?? I doubt that also.
     
  7. hmb

    hmb Well-Known Member

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    And don't forget to allow for the gravitation pull of the Moon. HMB
     
  8. Neil Winston

    Neil Winston Well-Known Member

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    I read that it's the primers. The author, a certified expert of a bygone era, said that when primers had fulminate of mercury consistency was much easier to attain. He said now that the Hg is gone, it's impossible to keep shots going the same speed like you used to be able to. This was by a guy who really, really did know what he was talking about.

    Neil
     
  9. Dr.Longshot

    Dr.Longshot Banned Banned

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    Pat Ireland SAAMI has tolerances of + or - 90 fps now that is a spread, take a New AA Super Hdcp + 90 fps and 1340 fps is legal.


    Gary Bryant
    Dr.longshot
     
  10. Neil Winston

    Neil Winston Well-Known Member

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    I wish you would quit writing that, Gary, You _know_ it's not true and still you repeat it endlessly. Why?

    Neil
     
  11. phirel

    phirel TS Member

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    Gary- It seems as if the ATA has tighter tolerances than SAAMI.
    Neil- Primers-- it certainly is possible but that suggestion is something I do not know how to confirm. How consistently can the wad skirt contain 9,000 pounds of pressure?

    Pat Ireland
     
  12. zzt

    zzt Well-Known Member

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    Pat, I don't measure that much variation in the factory shells I shoot (STS). Most often it's a total spread of between 25 and 30fps. The last 1oz batch I tested had an extreme spread of 23fps. I do recall Neil posting a chart showing some loadings from other manufacturers that were worse.

    If you cut open 10 Nitro 27s from the same box, and carefully weight all the components, you'll find the powder can vary by 0.1gr and the shot by 10 grains (sometimes more). Wads vary in weight by .2gr. Add in the primer inconsistency Neil just brought up.

    Add in wad obturation factor you just brought up. Factor in powder that clings to the hull wall and isn't scaped off when the wad is seated and you have quite a few variables. I used to wonder why there was such a "large" spread. Now I marvel they can keep it so close.
     
  13. shootsome

    shootsome Member

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    What's the max velocity ATA allows?
     
  14. hmb

    hmb Well-Known Member

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    As far as I know the ATA has no velocity testing protocol in place for checking ammo at registered shoots. HMB
     
  15. Paladin

    Paladin Well-Known Member

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    Along with the many variables listed above, the varying propellant pressure needed to overcome 'varying' crimps must also come in play.


    Rifle shells with the bullet crimped in can vary over 100 fps extreme spread, easily, recorded over an Oehler. Crimping a bullet in a brass casing is a quick way to introduce extreme spreads, because the crimps are seldom consistent, because the cases are seldom consistent.


    Factory crimped new rifle shells are the worst. A shotshell will probably share some pressure similarities.
     
  16. BDodd

    BDodd TS Member

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    To quote Col. Jeff Cooper;

    “Shooters, especially competition shooters, are often afflicted with Preoccupation with Inconsequential Increments.”

    <;-) BD
     
  17. Paladin

    Paladin Well-Known Member

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    From Wikipedia;


    Cooper defined his goal: "... a general-purpose rifle is a conveniently portable, individually operated firearm, capable of striking a single decisive blow, on a live target of up to 200 kilos in weight, at any distance at which the operator can shoot with the precision necessary to place a shot in a vital area of the target."


    Maybe Cooper wasn't big on "inconsequential" increments, but research and technology advancements are an important part of competition. It is one of the reasons high end manufacturers, and this web site are so successful.
     
  18. Jack L. Smith

    Jack L. Smith Member

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    Pat, you have previously supplied your own answer. Somewhere, a really big magnet is being turned on and off. Depending on the magnet position relative to the shot, this will effect the velocity. Quarks and neutrinos are also being effected.

    js
     
  19. Quack Shot

    Quack Shot Active Member

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    Neil Winston

    Was that authors name you refer to start with Earl? I remember a pretty detailed explanation I read about 40 years ago.
     
  20. redhawk44

    redhawk44 Member

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    If shot to shot variation of 35 feet pr second bothers you, then disregard it and start thinking about standard deviation.

    SD is usually about 1/3 of the hi and lo.
     
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