The I-301 was armed with one axial mounted MP-6 23 mm autocannon designed by Ya. Taubin which fired through a hollow propeller shaft in the "vee" between the engine cylinders and two synchronized Berezin UBS machine guns in the cowl. The MP-6 had 81 rounds of ammunition while the Berezin UBS had 230 rounds per gun. The MP-6 was abandoned after the prototype due to excessive recoil forces that damaged engine fittings. The I-301 used a Klimov M-105P engine of a licensed derivative of the Hispano-Suiza HS 12Y with a two-speed two-stage supercharger. At it was heavier than its competitors the Yak-1 and MiG-1, which meant its ceiling of was less than both. The I-301 took to the air for the first time on 30 March 1940 and by 12 June 1940 the manufacturer's tests were completed. The test pilot, A. Nikashin, reported that the fit and finish of the prototype was very good, it handled well, was maneuverable, and could be mastered by pilots of average ability.