At 49:48 they begin shooting an MG42 on full auto. The MG42 barrel would become too hot to sustain full automatic fire in as little as 6 seconds and the barrel would need to be changed.
At 48:42 they had been shooting an MG42 on full auto and told to hold fire, then at 48:49 there is no spent ammo belt being shown, and at 48:59 a spent ammo belt is now shown.