mcb
Member
It sort of funny. With internal ballistics you really want lower sectional density as this will tend to let you run faster burning powders making more efficient use of case volume resulting in higher muzzle velocities. As soon as we transition to external ballistics we want very high section density as high sectional density usually also means a reasonable high ballistics coefficients resulting in a flatter trajectory. As soon as we enter terminal ballistics on critters we want that sectional density to again be as low as possible without compromising bullet structure to make a larger wound channel.
As hunters we are pretty good at using bullets that go from high section density for the external ballistic phase and then transforming to low section density projectiles for the terminal phase. There has been some work going the other way mostly in military application but I have seen a few for civilian use also. Guns that are squeeze bore guns that start out with a low sectional density projectile and then squeeze the projectile up to a higher section density at some point down the barrel. Not sure I have ever seen it all brought together though since most military application want high section density in the terminal phase also as that is typically better at defeating armor.
rambling...
As hunters we are pretty good at using bullets that go from high section density for the external ballistic phase and then transforming to low section density projectiles for the terminal phase. There has been some work going the other way mostly in military application but I have seen a few for civilian use also. Guns that are squeeze bore guns that start out with a low sectional density projectile and then squeeze the projectile up to a higher section density at some point down the barrel. Not sure I have ever seen it all brought together though since most military application want high section density in the terminal phase also as that is typically better at defeating armor.
rambling...