Very Low Drag
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Very Low Drag Bullets, usually referred to by the abbreviation VLD, are primarily a small arms ballistics development of the 1980s - 1990s, driven by shooters' desire for bullets that will give a high degree of accuracy and kinetic efficiency, especially at extended range. To achieve this the projectile needs to be able to overcome air resistance in flight. This is inversely proportional to the deceleration. Demand has been most pressing from extreme accuracy target shooters, including benchrest competitors, but live-quarry game hunters have also benefitted.
Most VLD bullets are intended for use in rifles, and in all instances the intention has been to enhance accuracy by increasing bullets' ballistic coefficients and sectional densities, thereby improving the downrange retention of velocity and kinetic energy, flattening the projectiles' trajectories, and increasing their resistance to deflection by crosswinds.
The development of VLD bullets has focussed on the following main factors :
- the production of bullets with concentric and coincident centres of form and centres of mass
- bullet design incorporating a secant ogive, tangent ogive, Von Kármán ogive or Sears-Haack profile in the bullet's nose area
- the use of carefully tapered bullet heels or boat-tails
- a cavity or hollow in the bullet nose (hollowpoint) to shift the projectile's centre of gravity rearwards
Where a bullet is well manufactured and correctly balanced, with a aerodynamic nose, a tapered heel or boat-tail, and a hollow-pointed nose, the resulting projectile should be very "slippery" - i.e. well streamlined - for easy passage through the air, and have good down-range velocity and energy retention. Consistency in bullet production quality, allied to consistency in the assembly of cartridges - i.e. quality control - should give excellent shot-to-shot consistency.
The principles of bullet design and flight are classically set out in Mann, F.W.: The Bullet's Flight From Powder to Target: Ballistics of Small Arms (1942 and other reprints).
