Dimpled Bullets??

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    shadow116

    shadow116

    2nd Class Citizen
    Feb 28, 2008
    1,542
    Emmitsburg
    Anyone seen this?

    With equal-pressure loads, dimpled .308 bullets will fly about 80 fps faster than normal .308 bullets. With the large .338-caliber projectiles, the difference is even greater… we can pick up nearly 150 fps.
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    the Army tried a variety of designs, including bullets with circumferential drive bands, dual-radius ogives, and rebated boat-tails. The dimpled “golf-ball” design was considered a “long shot” according to the design team, but it has performed beyond all expectations. The nominal drag coefficient (Cd) has improved by about +.040, while cartridge muzzle velocity has increased by nearly 80+ fps because the bullet’s dimpled skin reduces in-barrel friction.
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    While the internal design and core materials of the new dimpled bullet remain classified, the design team revealed that the terminal performance of the new bullet has been “spectacular”. The bullet penetrates like a FMJ but then explosively fragments, resulting in a devastating energy release in the target. “Most FMJ bullets break along the cannelure and then fragment into two or three large pieces. With the dimpled bullets, you have multiple fragmentation points so the bullet literally blows up like a grenade in the target.”
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    http://accurateshooter.wordpress.com/2009/04/01/us-army-team-tests-radical-new-dimpled-bullet/
     

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    E.Shell

    E.Shell

    Ultimate Member
    Feb 5, 2007
    10,334
    Mid-Merlind
    If accuracy is acceptable, these would be a hoot.

    With regards to pressures vs velocity, Barnes has several designs that can be driven faster due to driving band design reducing the contact area.

    Berger's ballistician mentioned in the article, Bryan Litz, posts over at LongRangeHunting.Com and at BenchrestCentral.
     
    joppaj

    joppaj

    Sheepdog
    Staff member
    Moderator
    Apr 11, 2008
    46,704
    MD
    So we're taking up a collection to buy Ed a couple of boxes so we can get a test, right? :D
     
    DZ

    DZ

    Ultimate Member
    Oct 9, 2005
    4,091
    Mount Airy, MD
    Interesting idea, not sure what this would do to rotational stability since the bearing surface area is reduced. Would be nice if they talked about how much it raised the BC of their .308 projectile. If its on the same order of magnitude as the increase of the Cd, then Im going home and wacking a bunch of dents in my SMKs :sad20:

    If rotational stability is retained, shouldn't accuracy be the same if not better? Its been a while since I took fluid dynamics, but I think that having a turbulent boundary layer would would allow the bullet to "resist" slight changes in pressure, such as wind.
     
    E.Shell

    E.Shell

    Ultimate Member
    Feb 5, 2007
    10,334
    Mid-Merlind
    IDriveB5 said:
    Interesting idea, not sure what this would do to rotational stability since the bearing surface area is reduced.
    Click to expand...
    Rotational stability is independent of surface contact, since it is a product of gyroscopic (inertial) action, which can take place within a sealed container with no loss of effect.
    Would be nice if they talked about how much it raised the BC of their .308 projectile. If its on the same order of magnitude as the increase of the Cd, then Im going home and wacking a bunch of dents in my SMKs :sad20:
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    BC is inversely proportional to Cd, but I don't know what the numerical relationship is. Just saying it's 1:1, an increase in BD by .04 is substantial. The 175 SMK has a BC of about .495, so this would represent 8%, IF it is 1:1.
    If rotational stability is retained, shouldn't accuracy be the same if not better?
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    There are plenty of very stable bullets that are not accurate - pick anything that is light for the caliber and reduce QC. Accuracy is a product of uniformity with regard to balance, center of gravity vs center of mass and the base area must be uniform as to not leave the bore in a random direction.
    Its been a while since I took fluid dynamics, but I think that having a turbulent boundary layer would would allow the bullet to "resist" slight changes in pressure, such as wind.
    Click to expand...
    Reducing wind drift would be a huge plus.
     
    smokey

    smokey

    2A TEACHER
    Jan 31, 2008
    31,527
    if anyone wants, i'll swing by and dimple up your automobile to improve the aerodynamics of the ride and improve gas mileage...
     
    smokey

    smokey

    2A TEACHER
    Jan 31, 2008
    31,527
    leroygibbs said:
    Screw the ride, how 'bout my head to help with the aerodynamics when I walk?
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    my cranial aerodynamics have been constantly improving for the last few years every time i scratch my head or dry my hair with a towell.
     
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