Very-low-drag bullet
The very-low-drag bullet (VLD) is primarily a small arms ballistics development of the 1980s–1990s, driven by shooters' desire for bullets that will give a higher degree of accuracy and kinetic efficiency, especially at extended ranges. To achieve this, the projectile must minimize air resistance in flight. Demand has been greatest from military snipers, long range target shooters, including F-class and benchrest competitors, but hunters have also benefited. Most very-low-drag bullets are used in rifles.
Bullets with a lower drag coefficient decelerate less rapidly. A low drag coefficient flattens the projectile's trajectory and also markedly decreases the lateral drift caused by crosswinds. The higher impact velocity of bullets with low drag coefficients means they retain more kinetic energy.
Development
The development of very-low-drag bullets has focused on the following main factors:
- the production of bullets with concentric and coincident centres of pressure and centres of mass
- bullet nose design incorporating a secant ogive, tangent ogive, Von Kármán ogive or Sears-Haack profile
- the use of tapered bullet heels, also known as boat-tails
- a cavity or hollow in the bullet nose (hollow point) to shift the projectile's centre of gravity rearwards
- To reduce damage to the employed barrel and increase muzzle velocity, some modern mono-metal very-low-drag bullets are bore-riding bullets, in which thin driving bands are the only parts that are etched by the barrel's lands. The use of driving bands originates from artillery shells and to use these driving bands correctly requires projectiles and barrels to be precision-fitted to each other.
The resulting projectile should be streamlined for easier passage through the air. Consistency in bullet production, allied to consistency in the assembly of cartridges (quality control) should give excellent shot-to-shot consistency.
The principles of bullet design and flight are classically set out in F.W. Mann's The Bullet's Flight From Powder to Target: Ballistics of Small Arms.[1]
Modern design
The possibility to machine mono-metal bullets (coreless bullets made of one single metal (alloy)) offers bullet designers the freedom to design slender, aerodynamically efficient shapes that cannot be produced with more traditional bullet production methods.
Mono-metal very-low-drag bullets are normally machined from solid bars of highly-machinable metals or alloys using CNC lathes. Common materials include UNS C36000 Free-Cutting Brass, lead-free brass,[2] oxygen-free copper and other highly machinable alloys of copper, nickel, and tellurium.
Producing accurate bullets this way is not easy. To guarantee the bullets' consistency and accuracy, professional quality control during and after production is needed. Mono-metal solid bullets are more expensive than traditional jacketed Hollow Point Boat Tail very-low-drag bullets.
See also
- Drag (physics)
- Parasitic drag
- Boundary layer
- Drag coefficient
- Ballistic coefficient
- Nose cone design
References
 | This article needs additional citations for verification. (November 2011) |
- ^ * Mann, F.W.: The Bullet's Flight From Powder to Target: Ballistics of Small Arms (1942 and other reprints)
- ^ Wieland-SW1 lead-free special brass