Another note, even though the GAU-21 .50 cal is shown above, the GAU-2 (M134) 7.62mm minigun can also be used on the same mount.
Additionally, it is not unheard of (not common either) for an HH-60G to have a GAU-21 on one side and a GUA-2 on the other to give the crew more flexibility. Also, they usually travel in a 2 ship flight. One aircraft can be armed w/GAU-2s and the other armed with GAU-21s.
M240D 7.62mm MGs can also be mounted, but this is not as common.