Avery-low-drag bullet (VLD) is primarily asmall armsballistics development of the 1980s–1990s, driven by the design objective of bullets with higher degrees of accuracy and kinetic efficiency, especially at extended ranges. To achieve this, the projectile must minimizeair resistance in flight. Usage has been greatest from militarysnipers and long-range target shooters, includingF-class andbenchrest competitors, but hunters have also benefited. Most VLD bullets are used in rifles. VLD bullets typically have aballistic coefficient greater than 0.5, although the threshold is undefined.[1]
Bullets with a lowerdrag coefficient decelerate less rapidly. A low drag coefficient flattens the projectile'strajectory and also markedly decreases the lateral drift caused by crosswinds. The higher velocity of bullets with low drag coefficients means they retain more kinetic energy.[1]
VLD bullets are long and heavy for their diameter, to achieve a highsectional density.[1] Development of VLD bullets has focused on reducing a form factor defined as the sectional density divided by the ballistic coefficient.[2] Form factor can be minimized by:
The resulting projectile should bestreamlined for easier passage through the air. Consistency in bullet production, allied to consistency in the assembly ofcartridges (quality control) should give excellent shot-to-shot consistency.[citation needed]
The principles of bullet design and flight are classically set out inFranklin Ware Mann'sThe Bullet's Flight From Powder to Target: Ballistics of Small Arms.[4]
Machining mono-metal bullets (coreless bullets made of one single metal) offers bullet designers the freedom to design slender, aerodynamically efficient shapes that cannot be produced with more traditional bullet production methods. Professional quality control during and after production is needed to guarantee the bullets' consistency and accuracy. Mono-metal solid bullets are more expensive than traditional jacketed hollow point boat-tail VLD bullets.[citation needed]
To reduce damage to the employedbarrel and increase muzzle velocity, some modern mono-metal VLD bullets are bore-riding bullets, in which thindriving bands are the only parts that are etched by a barrel's lands. The use of driving bands originates fromartilleryshells and to use these driving bands correctly requires projectiles and barrels to be precision-fitted to each other.[citation needed]
Mono-metal VLD bullets are normally machined from solid bars of highly-machinable metals or alloys usingCNC lathes. Common materials include UNS C36000 free-cuttingbrass, lead-free brass,[5]oxygen-free copper and other highly machinable alloys ofcopper,nickel, andtellurium.[citation needed]