When Ing. Felice Trojani presented to the Regia Aeronautica tecnical staff the design of AUT-18 the Chief of staff, Gen. Cebrelli, protested: "We tested two MG under the wings of a CR and shooting was impossible, his wings proved not stiff enough." But Sir" was Ing. Trojani reply "the CR wing is probably a dozen centimeters high, my airplane wing is 37 cm high..."
Felice Trojani, La coda di Minosse, Ed. Mursia.
So I doubt that CR-42 has ever had underwing guns.