I was in the Army 1955-57, too late (thank God!) for the Korean war and too early for VN. But my platoon sergeant was a Korea vet and he told me something similar. He had been issued an M1 rifle, but it was heavy and at the first chance he threw it away and got a carbine. Then his Eighth Army unit got hit by one of the Chinese bugle-blowing attacks. He fired the carbine and it just didn't stop the enemy, due partly at least to their heavily padded winter clothing. As soon as possible, he threw away the carbine and got another M1.