In 1995, we proposed a non-destructive type of three-stage light-gas gun having an additional preheating and filling stage which allows to regulate in a broad range the initial energy of working gas. Installation and preliminary tests of the system were almost completed. In several shots as a conventional two-stage light-gas gun with unheated helium gas, a velocity of 6.49 km/s was achieved for 1.7-g projectile. In preheating tests, a 9.5-kg pre-pump piston was reusable under the condition in which He-gas was preheated to 1080 K by compressed air of106&hthinsp;Pa.A relaxation time of heat conduction loss through the pre-pump wall was estimated to be 96 ms from the pressure profile of He-gas confined. In the case of powder, the peak temperature of He was achieved to the value of isentropic compression, 1300 K, and was in good agreement with the value estimated from the sound velocity. From simulation, we propose the concept of operational mode limits that is the difficulty to regulate pressure/temperature profiles with time in the conventional gun, and the preheating effects can suppress these mode limits. ©2000 American Institute of Physics.