Base Burn is one method of extending the range
(or naval gunfire
s. The low pressure
area immediately behind the projectile's rear end is a primary source of drag
during flight. In addition, the turbulence
of the airstream curling in from the projectile's side to fill this gap causes drag, although the projectiles are 'boat-tailed
' to reduce this effect.
A base burn projectile contains a small pyrotechnic on the rear end of the shell that is ignited by the shot. It burns in a controlled fashion, and emits gases at a rate which raises the pressure in the area behind the shell. This lowered pressure differential between the front and rear allows the projectile to retain more kinetic energy, and hence travel further. This is distinct from base bleed and base boost projectiles.