Bullet Shapes / Aerodynamics

Discussion in 'The Ammo & Reloading Forum' started by Albtraum, Jun 7, 2013.

  1. Albtraum

    Albtraum Well-Known Member

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    I used to always think the sharper the nose, the more aerodynamic the projectile is, but isn't it the opposite? Since a water drop is the most aerodynamic shape produced by nature, a fluid that forms a big round front that tapers back to a thin point. Boat tail bullets have higher ballistic coefficient than flat ones, but what about the front of the bullet? Only round nose B.C. numbers I find are for old revolver and level action rounds. Would a .50BMG or .338 have an even higher Ballistic Coefficient if the nose was more round? Seems like the bullet would be more stable in flight too, since the drag would be at the rear, and not a pointy front.
  2. slayer

    slayer Active Member

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    A round nose bullet has more surface area. That's not a good thing. It creates more drag which isn't good. A round nose bullet drops faster than a spire point also no good for shooting long range. Take sports cars for example, corvette front ends are narrow not big and bulky like a truck. Less surface area plus less drag equals longer flatter trajectories.
  3. LDBennett

    LDBennett Well-Known Member

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    Albtraum:

    The measure of how aerodynamic a bullet is is the Ballistic Coefficient (BC). Thumb through a bullet manufacturers reloading manual and they will usually have BC's listed for each of their bullets. Long pointed bullets with a boat tail rear end usually have the highest BC. Among those, the shape of the nose of the bullet (the Ogive) can effect the BC. In no manual I have will a round nose bullet ever beat out a pointed nose bullet of the same weight for the BC.

    LDBennett
  4. Alpo

    Alpo Well-Known Member

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    What makes you think that a water drop is "the most aerodynamic shape produced by nature"? You say it as a given, like everyone knows that. Where is your proof?
  5. Zhurh

    Zhurh Active Member

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    To me, how they fly is less a factor than what damage they do when they hit their target. We've shot a bunch of caribou over the years and certain bullets are much more deadly than others and it's physical makeup is why. Just shoot some game with GMXs then go to Accubonds or TTSXs or Nosler Partitions; the GMXs seem to fly right but don't do much damage when they go through. Like a fool hunting with FMJs, no joke. What I can't figure out is why certain Gilding Metal (I think they are called) bullets seem to work satisfactory and others don't?
  6. Bindernut

    Bindernut Well-Known Member

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    Actually Albatraum the round-nose, pointy-tail water droplet is a fallacy.
    That's not how water forms itself when it's falling. It will look teardrop shaped as a piece of water is tearing away from whatever it was holding onto because it's trying to hold onto that surface due to surface tension. But once it's in freefall then surface tension pulls all the molecules in the droplet into a perfect sphere.
    As air friction works against the droplet the nice round nose will actually flatten out up front and can even go concave if the right conditions are met...the air won't just smoothly pass around it.

    Like LD said, check out the ballistic coefficient figures of assorted bullet shapes.
    A shallower tip angle allows the bullet to pierce through the air better...less friction and as the bullet goes supersonic the shockwave won't be buffeting the bullet either.
    A big flat or round nose doesn't cut the air as well so air friction does act on that style more than a pointed nose.

    A flat base also induces turbulence as the air wraps back around the bullet into the slipstream it created as it's moving. A boat tail design lessens that effect.
    Compare this to driving down the interstate and coming up behind a tractor pulling a reefer or other box van. If you get too close you'll start getting drawn up into that buffeting zone and it can chuck your car around pretty good. A flatbed trailer doesn't have as much flat surface out back so the buffeting behind it won't be nearly as bad. and even less so behind a little half-ton pickup or a car.


    And Zhurh makes a very good point when it comes to hunting bullets too. If you're shooting a long range match at paper targets, then the most aerodynamic bullet design you can use is probably the better choice. But for a hunting bullet you have to consider the terminal performance when it hits whatever game you're after too.
    Last edited: Jun 7, 2013
  7. LDBennett

    LDBennett Well-Known Member

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    A lot has been done to bullet performance in the last 25 years. Target bullets typically have have high BC's because that gives them the most flat shooting and the long range performance. But they are not good for hunting as they might go completely through a animal not releasing much of their energy on the game.

    To get clean game kills the bullet must enter the game and not exit it. That allows all the energy of the bullet to do its damage for a humane kill. The hole is not the reason the game is terminated but it is the damage inside the game that makes the kill fast and humane. To that end hunting bullets are made so they expand on impact and become larger in diameter to do the most internal damage. FMJ or pure target bullets might just pass through the game and give it a long suffering death and make you have to track it for miles until it dies of the blood lost. Not the right way to hunt.

    In short BC is not the answer by itself. It depends on the use for the bullet, so choose wisely. Most bullet manufactures offer lots of help in their reloading manuals as to what bullet should be used for what purpose.

    LDBennett
  8. Albtraum

    Albtraum Well-Known Member

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    Thanks it all makes sense. Especially the fact that a spire cone shape .338 IS more aerodynamic than a round 30-30. Sorry, just some late night rambling. However the Bugatti Veyron IS a very round car, with every square inch designed to be aerodynamic, to have a top speed of 253 mph...
  9. LDBennett

    LDBennett Well-Known Member

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    Albtraum:

    In the vehicle comparison, you don't see many 200+ MPH Bonneville cars in any shape other than pointy nose and long, narrow, and sleek. Cars like the Bugatti Veyron have to be street-able and utilitarian, and as such can not be long and narrow as the aerodynamics really dictates. The compromise is to keep the air from damming up in front of the car and give that air easy escapes around the car. They also feed air under the car to increase the down force and dump air behind the car to fill the vacuum created by the cars movement through the air, much as the boat tail on a bullet.

    The bottom line is long, narrow, pointed, and boat tailed is what gives bullet and cars the best aerodynamics. (Better yet the tail of the Bonneville cars is pointed too, to minimize the disturbance of the air it is passing thorough.)

    LDBennett
  10. Skipper

    Skipper Active Member

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    Nature's Spitzer Boattail


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