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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. KBO

    KBO New Member

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    Lets put it simple; if a bigger and heavier shell is propelled at 800m/s then that shell will be more effective than a similar but smaller shell propelled at the same velocity.
    Yes a bigger shell will have larger air resistance to deal with, but it also has a bigger mass to deal with that resistance, AKA kenetic energi.

    Man its hard to explain in english... :eek:

    KBO
     
  2. Notmi

    Notmi New Member

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    Why does 16" 2700 pounds AP shell travels over 10000 yards further than 8" 335 pounds AP shell althought both are fired with same muzzle velocity and 40 degrees elevation? And 5" 55 pounds shell lags more than 10000 yards from that 8" range with same elevation & MV.

    Those are quite rough examples but point is this: If you have same shaped shells, say 50mm and 100mm, larger one will travel further because mass goes up something like 8 times when shell diameter doubles.
     
  3. KBO

    KBO New Member

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    yeah exactly..!!!

    KBO
     
  4. Greg Pitts

    Greg Pitts New Member

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    You will need to provide more information that what you have shown in order to answer that one. I don't believe both fire at the same velocity in your example but have no source of information on large caliber naval gun ammunition.

    Suppose you provide some.
     
  5. Greg Pitts

    Greg Pitts New Member

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    All projectiles traveling through air are influenced by two primary forces:

    1. air resistance and
    2. Gravity.

    Projectiles vary in their ability to maintain proportions of their initial velocity against air resistance according to their sectional density and shape.

    A. Sectional density is the weight divided in pounds divided by the square of its diameter in inches.

    B. The better the aerodynamic shape, ie... ballistic coefficient, the better the performance.

    Perhaps this answers your question.

    :smok:
     
  6. Notmi

    Notmi New Member

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    I believe this was for me?
    I dont have any booksources (dont have money to buy decent ones and libraries dont have them either) but I have some websitesources, info there is composed by someone who knows far, far more than I about naval guns.
    Here are links about to those guns (having some info about shells too):
    16"
    8"
    5"

    Few notes:
    1) Both 16" and 8" shells are superheavy shells, they might have same shape but that 5" AAC Mark 49 definitely isn't.

    2) I choose those shells because they were just about first ones I found having same MV (2500 fps) and about same elevation angle.

    3) 16" shell is twice as long as 8" and weights roughly 8 times more.


    One more thing. I didn't remember to put final conclusion to that my previous post. So here it is: We have two identical shaped shells, first one is twice as long and has twice diameter than second. First one is about 8 times heavier than second one but it has only 4 times more cross-section area. Therefore its weight overcompensates its bigger airresistance. Therefore heavier shell will travel further.
    Thats why .30-06 bullet wont fly further than large naval shells, no matter how streamlined or high speed .30-06 bullet is.
    Hopefully this "info" is what you were looking for.
     
  7. KBO

    KBO New Member

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    I didnt know it was a question :eek:

    I read it as Fact.

    KBO
     
  8. Ricky

    Ricky New Member

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    A simple request

    could people please not quote the entire previous post during a running discussion like the one above. We can work out what you are replying to. :roll:
    If you think that it is unclear, quote relevant chunks for reference.
    Having to scroll through the same old list of quoted posts each time somebody posts a 3-word reply is most irritating :angry:
    It also makes for whacking huge long pages that take an age to scroll down, and are really quite unneccessary.

    This relates to all topics & members, not just those in this particular discussion...

    Ok, rant over - on with the discussion!
     
  9. KBO

    KBO New Member

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    Sure Ricky, im sorry i didnt think of it when i posted.. :(

    KBO
     
  10. Oli

    Oli New Member

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    Hmmm, maybe this needs summarising before it gets too involuted.
    The graph HAS to be for a particular gun and ammo/ propellant combination how otherwise would APDS work?
    As for "no need for anything bigger than 105mm" - pentration is afunction of impacting mass, velocity, diameter and projectile and target material densities (among other things). To get a better penetration (WWII) you can increase velocity - limited by propellant type, gun tube waer characteristics etc etc, or increase calibre for a heavier shot - hence the Soviet 122mm.
    A simple, wargames-level formula for shot impact velocity is to take a particular range increment, say 250 yards, and divide that by the shot calibre, to get a % decrease in velocity per increment.
    Example 50 mm will decrease by 250/50 = 5% per 250 yards, and a 125 (keep the numbers simple) only 250/125 =2% per 250 yards.
    Therefore
    Calibre Muzzle 250 500 750 1000 1250 1500 yards
    50mm 1000 950 903 857 815 774 735 m or ft/sec
    125mm 1000 980 960 941 922 904 886 m or ft/sec
    all numbers rounded. This not "accurate" but does illustrate the effect of sectional density (well not as such because it doesn't hold true for APDS/APFSDS, which would have higher/much higher sectional densities than a pure calibre/increment equation shows.
    So the advamtages come in with sub-calibre, less drag and higher sectional densities work in their favour, as do smaller impact higher giving a higher energy density upon impact.
    But back to the original question - roughly a 2% increase/ decrease in barrel length will give a 1% increase/ decrease in muzzle velocity, don't know how far down with a decrease works, but increasing barrel length only works up to a maximum of about 20% ~ 10% VO increase. FOR A GIVEN PROPELLANT & PROJECTILE MASS.
    Oli
     
  11. Tony Williams

    Tony Williams Member

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    It also doesn't work with lightweight tungsten-cored full-calibre shot - PzGr 40, APCR, HVAP - which lose velocity more quickly than with full-calibre steel shot (by how much depending on the weight of the total shot assembly).

    That depends on how close the original barrel was to the optimum length for maximum velocity. Generally speaking, barrels are made shorter than the optimum, because the cost and inconvenience of the extra length isn't worth the minor increase in velocity which would be achieved. That isn't necessarily the case, however.

    Tony Williams: Military gun and ammunition website and discussion forum
     
  12. Oli

    Oli New Member

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    Quote: It also doesn't work with lightweight tungsten-cored full-calibre shot - PzGr 40, APCR, HVAP - which lose velocity more quickly than with full-calibre steel shot (by how much depending on the weight of the total shot assembly).

    :kill: Forgot that one. All of the information I get on this and penetration mechanisms will be on my website. One day.
    Oli
     
  13. Oli

    Oli New Member

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    Did a little bit of work on this, using data I had to hand only (not at home for a couple of weeks), I plotted calibre length to muzzzle velocity for a range of anti-tank guns (including tank-mounted) for full calibre shot, APCR and APDS.
    One thing I hadn't noticed before was the diminshing returns on APDS... go figure.
    To illustrate one of Tony's points, that "spike" on the APDS at 48 calibres is the difference between 125mm 2A46 (Russian smoothbore) at 1756 metres/sec (all values are metric on the graphs) and the proposed Rheinmetall 140mm at 2200 metres/sec. Both at 48 calibres long. (My estimate of calibre length based on drawings I have - but it's 46-50 almost certainly).
    So for an increase of 12% in calibre there's a 25% increase in muzzle velocity, couple that with the increase in projectile mass - and whammo! Something you would not like to meet down a dark alley - or even 2000 metres away in broad daylight.
    Hope this is of some use.
    Trend lines added by Excel (exponential values).
    Oli
     
  14. Tony Williams

    Tony Williams Member

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    Nice graphs. I thinkyou'll find that the reverse relationship for APDS/APDSFS is to do with the characteristics of the individual guns than a general truth.

    Tony Williams: Military gun and ammunition website and discussion forum
     
  15. Oli

    Oli New Member

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    Thanks.
    Here's the data I used:
    Designation Cal L/ V0
    6 pounder 57 45 1220
    2A46 125 48 1756
    Rh140 140 48 2200
    77mm 76.2 50 1120
    3.7" 93.98 50 1580
    120 L/52 120 52 1790
    17 pr 76.2 55 1037
    D-70 85 55 1070
    L11A5 & L30 120 55 1370
    Rh120 L/55 120 55 1750
    L7 105 57 1170
    T5E1 105 67 1128
    20 pounder 84 69 1478
    And (as posted in the wrong topic!!) I forgot the Rh120 L/44 (1670 m/s).
    Revised graph attached. Will do more work on this when I get back to my notes next week.
     

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