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How did base-bleed shells increase the range of artillery projectiles?

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Base-bleed shells increase the range of artillery projectiles by reducing aerodynamic drag during flight. In this system, a small compartment located at the base of the shell is filled with a smokeless propellant that burns throughout the projectile's trajectory.1

As the shell travels through the air, the combustion of this propellant releases gases that fill the vacuum created behind the projectile. By filling this low-pressure area, the base-bleed mechanism significantly decreases the aerodynamic drag that would otherwise retard the shell's motion. This process allows the projectile to maintain its velocity more effectively, resulting in an increase in range of approximately 25 to 30 percent compared to conventional shells. Unlike rocket-assisted projectiles, which require significant internal space for a motor, base-bleed units are more compact and preserve more room for the shell's payload.21