  In this paper we consider mid-infrared Raman lasers based on gas-filled
hollow-core silica fibers and provide theoretical and experimental analysis of
factors that limit the efficiency and output power of these lasers. As a
result, we realized an efficient ns-pulsed 4.42 {\mu}m Raman laser based on an
1H2-filled revolver silica fiber. Quantum efficiency as high as 36 % is
achieved, and output average power as high as 250 mW is demonstrated. The
possibilities of further improving the laser efficiency are discussed.
