Abstract: An intermediate actuating metal bellows filled with a liquid is positioned between an explosive gas cartridge and an actuating piston in an ordnance ejector system. The bellows is miniaturized, light weight and of low spring rate. The liquid in the bellows creates a fluid pressure internal to the bellows equal to the gas pressure external to the bellows, and is of low compressibility, low viscosity, low coefficient of thermal expansion, wide operating temperature range and high thermal conductivity. The fluid-filled bellows transmits gas pressure to the piston but prevents damage to the piston and piston seals from the high-pressure, high-temperature erosive gas. The liquid in the bellows acts as a heat sink to protect the bellows; as a heat insulator reducing heat losses to the piston housing and insulating the piston and piston seals from high temperature; and as a lubricant for the piston and piston seals. Environmental pressures and temperatures of 18,000 psi and 4500.degree. F.