3 ms·

The design of the bullet itself is interesting. Normally, longer and thinner is more aerodynamic, in any fluid, air or water - it creates less turbulence and d

The design of the bullet itself is interesting. Normally, longer and thinner is more aerodynamic, in any fluid, air or water - it creates less turbulence and drag. But here they found shorter and fatter works better for transonic projectiles: > The .416 Barrett cartridge is made by “necking down” a .50 Browning Machine Gun (BMG) round to accommodate the roughly .40-caliber bullet. It’s a relatively short, stout bullet that proved ideal for its purpose, Humphries said. > “Traditionally in extreme long-range shooting, we wanted long, skinny bullets,” he said. “However, we discovered that as a bullet crosses over into subsonic velocity, it flies better if it’s shorter and fatter.”

colechristensen 4y ago
Bullets in flight have a few dynamical modes where they have a sort of wobble around the direction of travel. They all, when given enough distance, end up tumbling end over end which absolutely ruins accuracy though getting hit with a tumbling bullet is quite destructive for soft targets. I can totally see trying for a record being helped with a low aspect ratio bullet (er, short and stubby) though this is probably not what you’d actually do if you were doing anything but trying for records. Fun fact: if you don’t correct for the fact that the earth is spinning which requires knowing your latitude and compass direction, your targeting will be off by an amount measured in feet at this range. I spent a while developing external ballistics models for a similar use case years ago. The standard tome of knowledge is McCoy - Modern Exterior Ballistics https://a.co/d/8B6w0qL https://a.co/d/8B6w0qL
- jcims 4y ago
  Would you happen to know why so many high speed videos of bullets show them flying pitched up or down slightly from the direction of flight shortly after leaving the muzzle?
  - colechristensen 4y ago
    Those are just the dynamics. The angle of attack sort of wanders around the direction of travel, this is the basics of how rifiling helps stability.
    - jcims 4y ago
      That’s wild. I’ve seen it so many times, but I’ve never seen it discussed anywhere. Thanks!
      - colechristensen 4y ago
        You know how a train has angled wheels on each side so any perturbation will naturally cause the wheels to turn back towards the center? It's kind of like that. A perturbation away from the center causes a force to return towards the center but it's not damped all the way so there's a persistent wave motion back and forth at a characteristic frequency. A bullet is like that but has more degrees of freedom so there are a few of these kinematic modes happening at the same time.
        jcims 4y ago
        I don’t know why but that just gave me a whole new perspective on what’s happening in flight. I had been thinking of the visually perceptible motion but that made me think of the forces at play while it’s basically in freefall spinning in a slippery pocket of air. Everything happens so fast it’s easy to forget that physics is still happening one molecule at a time.

colechristensen 4y ago

Bullets in flight have a few dynamical modes where they have a sort of wobble around the direction of travel. They all, when given enough distance, end up tumbling end over end which absolutely ruins accuracy though getting hit with a tumbling bullet is quite destructive for soft targets. I can totally see trying for a record being helped with a low aspect ratio bullet (er, short and stubby) though this is probably not what you’d actually do if you were doing anything but trying for records. Fun fact: if you don’t correct for the fact that the earth is spinning which requires knowing your latitude and compass direction, your targeting will be off by an amount measured in feet at this range. I spent a while developing external ballistics models for a similar use case years ago. The standard tome of knowledge is McCoy - Modern Exterior Ballistics https://a.co/d/8B6w0qL https://a.co/d/8B6w0qL

jcims 4y ago
Would you happen to know why so many high speed videos of bullets show them flying pitched up or down slightly from the direction of flight shortly after leaving the muzzle?
- colechristensen 4y ago
  Those are just the dynamics. The angle of attack sort of wanders around the direction of travel, this is the basics of how rifiling helps stability.
  - jcims 4y ago
    That’s wild. I’ve seen it so many times, but I’ve never seen it discussed anywhere. Thanks!
    - colechristensen 4y ago
      You know how a train has angled wheels on each side so any perturbation will naturally cause the wheels to turn back towards the center? It's kind of like that. A perturbation away from the center causes a force to return towards the center but it's not damped all the way so there's a persistent wave motion back and forth at a characteristic frequency. A bullet is like that but has more degrees of freedom so there are a few of these kinematic modes happening at the same time.
      - jcims 4y ago
        I don’t know why but that just gave me a whole new perspective on what’s happening in flight. I had been thinking of the visually perceptible motion but that made me think of the forces at play while it’s basically in freefall spinning in a slippery pocket of air. Everything happens so fast it’s easy to forget that physics is still happening one molecule at a time.