A traveling charge is an additional explosive charge attached to the bottom of the projectile so that it travels with the projectile inside the gun barrel while burning. The concept was proposed by H. Langweiler in 1939.
See also Base bleed Caseless ammunition Gyrojet Rocket-assisted projectile
References
Further reading TRAVELING CHARGE COMPUTATIONS -EXPERIMENTAL COMPARISONS AND SENSITIVITY STUDIES, US ARMY BALLISTIC RESEARCH LABORATORY, TECHNICAL REPORT BRL-TR-2844, August 1987