The activity of development a COIL with high potential recovered pressure, high gain and efficiency is described. Two nozzle banks with conical supersonic nozzles for the driver nitrogen but with different nozzle arrangements have been developed for generation of the gain flow of chemical oxygen-iodine laser. The nozzle banks were supplied by oxygen flow from the cross-flow singlet oxygen generator with filament-guided jets. Results of aerodynamic tests, visualization of flows by laser induced fluorescence, scanning of the excited iodine atoms distribution and laser power extraction are presented. The efficient penetration of the driver buffer flow into the gain flow was observed at distances less than 100 mm from the nozzle banks. The total power exceeding 1 kW with chemical efficiency more than 24% was obtained in 5 cm gain length COIL without helium dilution. The lasing was observed for both nozzle banks at total mirror transmission more than 10%.