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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. Christian Ankerstjerne

    Christian Ankerstjerne Member

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    I think that Tony means, that if you have a gun og a given size, and then enlarge everything in the same proportion (e.g. 2:1), then the muzzle velocity will increase.

    This makes sense to me, since the amount of gun powder in increased by the power of three of the increase in caliber (for example, if the caliber is doubled, the amount of gun powder is multiplied with eight).
     
  2. KBO

    KBO New Member

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    I guess a little Danish came into that speach........ :lol: :lol: :lol:

    Best regards, KBO
     
  3. Tony Williams

    Tony Williams Member

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    What I meant was that if you have a 90mm gun firing a 10 kg shell with 5 kg of propellant, it will achieve a higher muzzle velocity than a 75mm gun firing a 10 kg shell with 5 kg of propellant. The larger bore diameter enables the propellant to be used more efficiently.

    Tony Williams: Military gun and ammunition website and Discussion forum
     
  4. Greg Pitts

    Greg Pitts New Member

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    Tony, You are assuming the same type of projectile and propellant in this instance are you not?

    This one is food for thought and I will have to do some research. Right off the bat, I'd say this is not true. Will have to go to the books on this one.

    :wink:
     
  5. Greg Pitts

    Greg Pitts New Member

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    Tony,

    One small arms evaluation:

    .270 (.277 diameter) Winchester 110 grn jacketed spitzer 37 grns of RX-7 = 2876 fps
    30-06 (.308 diameter) Springfield 110 grn jacketed spitzer 37 grns of RX-7= 2736 fps

    Both rifles have a 1-10" twist. Barrel length on .270 is 26" and 30-06 is 24". Both are universal receivers.

    The barrel length will account for some of the difference if not all, but this shows that a larger caliber shooting the same projectile and with the same powder charge, will not neccessarily have a higher velocity. Length of barrel is a factor I did not see mentioned in the previous post.

    I could not find an example with same length barrels but will keep looking.

    The principle will remain the same whether we are talking rifles or larger weapons.
     
  6. Tony Williams

    Tony Williams Member

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    The example you quote may simply be due to the fact that the rifle powders used are less suitable for extracting the most fom a light bullet in the .30-06 case.

    A more relevant comparison would be to look at typical or average muzzle energy levels for cartridges of the same size but of different calibres. For example, all of those below (taken from 'Gun Digest' tables) are based on the .30-06 case:

    .25-06 = 2,300-2,400 ft lbs muzzle energy
    .270 = 2,600-2,700
    .30-06 = 2,700-2,900
    .35 Whelen = 3,200

    That proves my point, I think.

    To go back to the tank gun issue: the whole point of subcalibre projectiles is to combine a small calibre for penetration with a large calibre barrel to get the most out of the propellant. The tungsten alloy penetrator of the 17 pdr APDS shot is only 38mm in diameter. If it were fired (without the sabot) from a 38mm calibre barrel with the same propellant charge, it wouldn't travel anywhere near as fast.

    Tony Williams
     
  7. Greg Pitts

    Greg Pitts New Member

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    Then your point is different than in your previous post. Your previous post said nothing about foot punds of energy. As for the sabot round you mention, that is a whole different ballgame. The smaller projectile with the sabot can achieve much higher velocities due to increased propellant capacity in the larger caliber weapon. This velocity will fall off much, much quicker that the previously mentioned round, as well.

    The smaller caliber weapon without sabot will never be able to hold a propellant charge as great as the larger caliber weapon using the sabot (assuming conventional gunpowder propellants).

    That's an apples & oranges comparison.

    I also do not understand what you mean when you say that the different calibres you mention with ft lbs of energy are all based on the 30-06 case?

    " 25-06 = 2,300-2,400 ft lbs muzzle energy
    .270 = 2,600-2,700
    .30-06 = 2,700-2,900
    .35 Whelen = 3,200"

    Again, in all of these examples, powder charge will directly affect the stated ft lbs of energy.

    A .30 caliber carbine with a 110 grn bullet gives off roughly the same ft lbs of energy at the muzzle of a .44 mag pistol. So??????????

    What's your point here?
     
  8. Mutant Poodle

    Mutant Poodle New Member

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    Re: The relationship between muzzle velocity and barrel leng

    Ya know, when I see this graph I can see why this post WW II tank commander said to me that there is no need for any MBT MG to be over a 105 mm. It is the type of round and quality of the projectile that destroys the target.

    Nice graph.
     
  9. Tony Williams

    Tony Williams Member

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    Foot pounds of muzzle energy are a more convenient measure of the power of a cartridge. If you have bullets at the very high or very low end of the weight range for a calibre (e.g. 110 grains in a .30-06), you may not get the best efficiency as the powders available may not be optimised for such cases. A more relevant test could be to try the .270 against the .30-06 when both are loaded with 140 grain bullets, as this is within the normal range for both calibres. You will see that the .30-06 can be loaded to higher velocities within the same pressure ranges.

    I'm talking about the same propellant capacity firing the same weight projectile in large and small calibre weapons. This is easily possible, all you need is the same size cartridge case but with the neck sized to different calibres (in civilian rifle terms, think of the big Weatherby Magnum case which is used in calibres from .50 down to .30). You won't get the same velocity out of the small calibre weapon, because the bore is too narrow.

    Look at it this way: the chamber pressure is the limiting control over the power you can put behind a projectile - too much and the gun will blow up. So you've got a limit of, say 60,000 psi (that's a bit hot). Now if your projectile has a base area of one square inch, the propellant can only exert 60,000 lbs of pressure to push it up the barrel. But if the calibre is increased so that the base area is two square inches, then there's 120,000 lb of push.

    That's why the squeezebore guns were briefly popular; they had a large initial calibre so that the propellant gas had a big area to push against, but then tapered down to a small calibre at the muzzle so that the projectile was narrow. This meant it wouldn't slow down so much in nthe air and would punch through more armour.

    It's also why the British necked-up the 20 pdr (83.5mm calibre) tank gun to 105mm. The case held no more propellant - in fact it was slightly shorter - but the larger calibre allowed it to develop more muzzle energy and it therefore worked better with APDS rounds.

    Clear enough, I would have thought. Take some .30-06 cases and vary the neck diameter by squeezing down to .27 or .25, or by opening it up to .35. Leave the powder capacity of the case the same. Load with a similar amount of powder in each case, to develop the same sort of pressures. Load bullets within the normal weight range for the calibre, then measure the results. You will find that the larger the calibre, the higher the muzzle energy, because the larger bore makes more efficient use of the powder.

    Tony Williams
     
  10. Greg Pitts

    Greg Pitts New Member

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    Ok - that is what I thought you meant but I wanted to be sure, and we have already seen that what you say on this is not neccessarily the case; no pun intended.

    I will do some aditional research on avrious cartridges and see if I can find any loads that support your claim.

    :smok:
     
  11. Tony Williams

    Tony Williams Member

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    You needed search very far, I can provide you with some :)

    This is manufacturers' data from the ammunition columns of 'Gun Digest':

    .25-06 = 120 grains at 2,990 fps
    .270 = 135 grains at 3,000 fps

    .270 = 150 grains at 2,850 fps
    .30-06 = 150 grains at 2,910 fps

    .30-06 = 220 grains at 2,410 fps
    .35 Whelen = 250 grains at 2,400 fps.

    As you can see, in each pair of cartridges/loadings, the larger calibre has the power advantage despite the equal size of the propellant capacity.

    I can give you some examples from larger calibres as well. Take a look at the middle batch of four cartridges in the photo below (from the article 'Military Cartridge Relationships' on my website); they are all based on the same cartridge case with virtually identical powder capacity. The actual muzzle energies developed are as follows:

    15.2x114 (.60) = 46,000 j
    12.7x114 (.50/60) = 30,000 j
    20x102 (Vulcan) = 54,000 j

    Once again, a larger calibre = more 'piston area' = more efficient use of propellant = greater power.

    You can argue all you like, Greg, but you can't defeat physics :). The only exceptions to this rule (operating pressures and barrel lengths being equal) would be if the bullet loading was unusually heavy or light, in which case the commercial powders available might not be able to extract the maximum power from the case capacity. Also, very heavy and long bullets may need to be seated deeper in the case thereby leaving less room for powder.

    Tony Williams

    [​IMG]
     
  12. Greg Pitts

    Greg Pitts New Member

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    Tony,

    With all due respect, the examples you list are worthless.

    You do not list manufacturer, nor gunpowder type or charge, and in one of your examples, the larger caliber has a lower velocity. You also compare projectiles of different weight.

    I will go to my own information. I have reloaded ammunition for over 30 years, so you will forgive me if I am somewhat sceptical of what you are saying.

    The 30 minutes I took to look up a few stats showed me your information was incorrect but as I stated, I will do further research to see if any calibers support your claims.

    :wink:
     
  13. Tony Williams

    Tony Williams Member

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    The examples I quoted are of standard manufacturers' loadings, which will be loaded to standard pressures. The reason I didn't quote the same bullet weights is that the data sheets didn't provide them, so I picked the nearest. The ONLY case in which the larger calibre loading is fractionally slower is where it is firing a heavier bullet (didn't you notice that?), so the power developed is still greater.

    Greg, I notice you have completely ignored all of the other reasons and examples I have given in support of demonstrating the simple truth that, other things being equal, a larger calibre will extract more power from a given quantity of propellant than a smaller calibre. I don't think that there is much point in my continuing this debate, as my head is getting brick-scarred.

    Tony Williams: Military gun and ammunition website and Discussion forum
     
  14. Greg Pitts

    Greg Pitts New Member

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    I agree Tony. Your statements are incorrect and I see absolutely no reason to continue the discussion. You have quoted unsubstatiated figures and statistics with all pertinent data that is needed for analysis omitted.

    Unless you are willing to quote some meaningful and verifiable statistics, we're done. As it stands, all you have provided is hearsay. When you get some information you can validate, let me know.

    I will be glad to carry this exchange onwards without an audience.

    watcher1@airmail.net

    :smok:
     
  15. Mutant Poodle

    Mutant Poodle New Member

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    Can either of you two claim your information is infalible?
     
  16. Greg Pitts

    Greg Pitts New Member

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    My comments on this subject are based on 1st hand knowledge and reloading manuals in my possession. My learned colleague throws out information completely unsubstantiated and does not give reasonable comparisons, nor required information for reasonable analysis of what he states.

    We have an old saying in the South, "Don't piss down my back and tell me it's raining".

    :smok:
     
  17. Greg Pitts

    Greg Pitts New 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”

    Christian,

    I had a few minutes and wanted to address “air Resistance” and a few other notables on trajectory factors. Air resistance in relation to ballistics is quite an important factor. When we walk around, we don’t feel much air resistance. If we run, we can feel the wind against our bodies. If we walk into a 40 mph headwind, we can significantly feel it. With winds of 150 mph railroad tracks have been twisted around trees.

    The .22 caliber bullet travels at approximately 11 fps, which corresponds to about 752 miles per hour. The 30-06 bullet starting at 2,700 fps encounters a gentle breeze of some 1,841 miles per hour, and reduces the velocity to 2,460 fps at 100 yards, 2,240 fps 200 yards, and 1,068 fps by the time it has reached 1,000 yards.

    Air resistance is a major factor in bullet/projectile performance.

    Gravity is also significant. A projectile, or most any body for that instance, falls 32.2 fps in the first second. The velocity increases at a uniform rate and will fall at 64.4 fps at the end of two seconds. The average velocity in the first second is 16.1 fps so at the end of two seconds, it will have fallen 48.3 feet. The average rate of fall for an object for any second is the average of the velocity at the beginning and the velocity at tghe end of that second. (Air resistance will affect this).

    In addition to air resistance and gravity, wind will cause the bullet to drift in proportion to the velocity and direction of the wind.

    Additionally, in rifles, there is a tendency fo a bullet to drift slightly to the right of the plane of fire if the bore is rifled with a riught hand twist, and to the left if there is a left hand twist.

    Yaw is another factor. If a bullet is slightlu unbalanced when it leaves the muzzle, it is not flying strictly with its point to the front but with an air spiral and may not steady down its flight until ot has passed 100 yards. Normally, yaw subsides by the time a projectile has reached 200 yards. Other terms for this are wabble, tip, and air spiral.

    Even outside temperature will affect projectile velocity. In higher temperatures velocity increases slightly. An average rule of thumb (Using 70 degrees as a base) for a rifle is that 1 degree Farenheight will cause a 1.5 fps change in velocity. A change of 20 degrees will significantly affect an impact point. To boot, temperature affects powders with nitro-glicerin and nitro-cellulose more than single base powders that contain nitro-cellulose powders alone. The loss in velocity due to a change in temperatire from plus 70 degrees to minus 40 degrees F can be from 3 to 5 percent.

    Lastly, let’s look at shooting up or down slopes. A slope of ten degrees or less has little affect here. A distance that is 100 yards on the level will be 150 yards on a slope of 45 degrees. The problem becomes one of estimating target height as a target that is 15 inches high at the verticle is only 10 inches high when looking at it either up or down at a slope of 45 dregrees. If we were shooting straight up or down, and the 100-yard elevation were 3 minutes there would be no drop of the bullet (from gravity) from the base line. Therefore, on averticle range of 100 yards, our bullet, in this example, will strike 3 minutes, or 3 inches, away from the base line and our point of aim.

    Thus, between a 10 degree slope and a verticle slope of 90 degrees there is a tendency to overshoot, being zero at 10 degrees and then increasing proportionally up to 90 degrees where it amounts to the change caused by the full angle of elevation at which the rear sight is set.

    Over a slope of 400 yards, with the sights set on a 30-06 for that distance, the sights would be set at an angle of 11 minutes. Firing vertically at 90 degrees, the bullet will strike 44 inches away from the base lone. On a slope of 50 degrees, it would overshoot 22 inches. At 200 yards, and an elevation of 5 minutes, it would overshoot 5 inches. On a 30-degree slope at 200 yards, the 30-06 rifle will overshoot 2 ½ inches.

    That’s it for now.

    (Source “Small Arms Design and Ballistics – Volume II – Ballistics” by Townsend Whelen


    :smok:
     
  18. Christian Ankerstjerne

    Christian Ankerstjerne Member

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    I agree that air resistance as a whole is important, however I was referring to the air resistance presented prior to the grenade leaving the barrel. The air resistance for these less than ten meters is not very important for the muzzle velocity. After all, the grenade can only go one way (unless the barrel cracks or the gun lock fails), and have a very high pressure behind it compared to the one in front of it.
     
  19. KBO

    KBO New Member

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    The air resistance might be higher for a higher calibre shell, but the weight of the shell is also bigger meaning air resistance has less effect...

    So air resistance and the weight of the shell rules each other out...

    KBO :D
     
  20. Greg Pitts

    Greg Pitts New Member

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    KBO, you couldn't be more wrong.
     

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