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The relationship between muzzle velocity and barrel lenght ?

Discussion in 'The Guns Galore Section' started by Skua, Sep 13, 2004.

  1. Skua

    Skua New Member

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    I found this graph showing the relationship between muzzle velocity and barrel lenght in calibres. It suggests that the pay-off is in muzzle velocity is quite good up to about 75 calibres in lenght, but decreases rapidly from there on. Little or nothing seems to be gained from increasing the barrel lenght beyond 100 calibres, but then few tank guns was more than 70 calibres long.

    I was just wondering if anybody could comment on the accuracy of this graph ? And if the relationship between lenght and muzzle velocity is constant, not influenced by the weight of the projectile etc. ?
     
  2. Greg Pitts

    Greg Pitts New Member

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    Something is missing in the equation...

    Such a graph cannot be "all encompassing". This impresses me as a graph on a particlar gun and ammo. It cannot be a graph that encompasses all guns and ammo.

    There are too many variables.

    Out of curiosity, where did you find it?

    :smok:
     
  3. Christian Ankerstjerne

    Christian Ankerstjerne Member

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    I think that the graph is likely to be reasonable accurate, but not in teh way it is presented. Two two most important other factors would be powder charge and projectile weight, however there are other factors as well.

    A specific barrel length will by no means guarentee a certain muzzle velocity. If that was the case, there would be no need for a powder charge. According to the graph, simply adding a barrel is enough to lauch the projectile, without any propellent.

    I do think that the graph could be converted into a modifier graph, so that it can be used in conjunction with other factors to give an estimated muzzle velocity.
     
  4. Greg Pitts

    Greg Pitts New Member

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    Exactly my point and is why I think the graph is for a particular weapon.

    :wink:
     
  5. GP

    GP New Member

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    What it could be (and this is only a thought) is a graph to show the maximum muzzle velocity attainable by the length of barrel, for a specific distance and accuracy, the latter 2 not stated.
     
  6. Skua

    Skua New Member

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    I found it in Peter Gudgin´s book "Armoured Firepower" ( Sutton Publishing Ltd, 1997 ).

    Unfortunately, he doesn´t go into detail regarding the graph. The caption, however, states that the graph was originally published in the Nachrichtenblatt der Panzertruppen, which might suggest that it only served an educational purpose. It does look a bit rudimentary.
     
  7. Ricky

    Ricky New Member

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    Probably a 'generic' example to illustrate how the equation works (possibly by using 'real' results) rather than an exhaustive scientific-type piece of information?
     
  8. KBO

    KBO New Member

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    Its a graph for German gun "Only"


    Regards, KBO
     
  9. Christian Ankerstjerne

    Christian Ankerstjerne Member

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    That is still not enough to explain the graph, with the values given.

    Looking closely on the graph, at zero calibers, the muzzle velocity is more than zero. This makes it even more absurd, as it would mean that a grenade will be in motion at any given time, wheter it has been fired or not.
     
  10. Ricky

    Ricky New Member

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    I was assuming that the graph was for a shot that had been fired. After all (as was pointed out above!) just because you have a long barrel does not make the shell move.

    So, you fire a shell through a barrel of 0 calibers, it will have thus much less muzzel velocity than if you fired through a barrel of 30 calibers length.

    And so on.
     
  11. Christian Ankerstjerne

    Christian Ankerstjerne Member

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    Still, the graph mentions nothing about weigh of the shell or amount of propellant. Thus, if the graph is valid, it is true regardless of these factors, and a grenade with no propellant will be fired at the same speed as a grenade with a infinite amount of propellant.
     
  12. Ricky

    Ricky New Member

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  13. Tony Williams

    Tony Williams Member

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    To clarify: there are three interrelated factors which determine muzzle velocity:

    1. Shell calibre and weight
    2. Propellant type and weight
    3. Barrel length

    You can only draw a curve for the effect of changes in barrel length for one particular combination of shell+calibre+propellant weight. If any of these factors is changed, the curve will be different.

    So you could, for example, draw such a curve for the Panther's 75mm L70 gun and AP ammo. However, the curve for the Pz.IV's 75mm L43/48 gun would be different as the cartridge case is smaller with much less propellant. And the curve for the early Pz.IV's 75mm L/24 would be different again.

    This is because the small quantity of propellant for the 75mm L24 gun burns out quite quickly, before the shell has travelled far up the barrel. So if you were to fire this round in an L70 barrel, the shell would probably be slowing down before it reached the muzzle so may have a lower velocity than for the L24 gun.

    To sum up, each calibre+shell+propellant weight combination will have its 'ideal' barrel length at which it develops maximum muzzle velocity. Much beyond that the shell will start slowing down again as the friction with the barrel becomes greater than the push from the propellant gas.

    Tony Williams: Military gun and ammunition website and discussion
    forum
     
  14. Ricky

    Ricky New Member

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    So, to sum up, this is probably a 'generic' example to illustrate how the relationship between barrel length and muzzle velocity works...
    :roll:
     
  15. Christian Ankerstjerne

    Christian Ankerstjerne Member

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    No, because it had fixed values. If it didn't have any values, then maybe.

    By the way, Tony, when dealing with the barrel length in calibers, does the caliber still have any impact on the muzzle velocity?

    Christian
     
  16. Ricky

    Ricky New Member

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    Sorry, I forgot to add 'probably using a specific, yet unnamed example'
    I've only put it twice before... :wink:

    But more importantly, if you have a graph without figures down the side, it does not really give the best idea of how this relates with that. For example, the increases of muzzle length could be in millimetres and the increases in velocity could be in 1,000,000 metres per second.
    (ok, yes, it says 'feet per second' and 'calibers', but the units - 1,000s of feet and increments of 25 calibers - are unknown, so the principal is the same.)
     
  17. Greg Pitts

    Greg Pitts New Member

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    Christian - If you mean will the gun caliber have an effect, the answer is yes. The larger the caliber, the more air resistance. It is still a relative issue however.

    If you mean caliber length of the barrel, the answer is yes again, but in any event, the items listed by Tony above are right on.

    "To clarify: there are three interrelated factors which determine muzzle velocity:

    1. Shell calibre and weight
    2. Propellant type and weight
    3. Barrel length "

    Given these items, there is a maximum for each caliber that can be obtained due to pressure limitations of the weapon. When muzzle velocities are pushed to the extreme in the gun by increased powder charge, barrel life is shortened (assuming pressures are within the gun's limits so it does not blow up).

    This will vary by ammunition type as well. Copper jacketed is most common. Lead alloy cast bullets are great but will cause "leading" at velocities above 1,000 fps. Paper-patch is a way around this and can allow you to shoot lead alloy bullets with high velocity.

    For small arms information you can obtain a number of reloading manuals that will give you a ton of information. Lymon, Speer, Hodgdon, & Hornady are 4 examples.

    :wink:
     
  18. Christian Ankerstjerne

    Christian Ankerstjerne Member

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    Greg, obviously a larger caliber shell will need to displace a larger amount of air (as far as I can figure out, the air displaced by the shell when exiting the muzzle is ((C / 2)² * π * L), where C is caliber and L is length of barrel. This also means, that the amount of air which has to be displaces increases with the cube of the caliber increase, if all other factors are the same.

    The amount of air displaced is still quite small, though. For example, an 8,8 cm. L/71 will only have to displace 38 liters of air - I don't see how this can be a very important factor...

    Christian
     
  19. Tony Williams

    Tony Williams Member

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    One interesting point is that for a given shell weight, propellant weight and barrel length, the muzzle velocity will go up with the calibre. This is because the shell in the barrel acts like a piston in a car engine; and the bigger the piston, the more efficiently it can use the propellant.

    If you look at the muzzle energies developed by rifle cartridges of different calibres based on the same case, you will usually find that they increase with calibre; e.g. the .30-06 is more powerful than the .270.

    More on this at: http://www.quarry.nildram.co.uk/ballistics.htm

    Tony Williams: Military gun and ammunition website and Discussion forum
     
  20. Ricky

    Ricky New Member

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    For clarification - do you mean that the propellant weight increases in proportion to the size/weight of the shell?
     

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