While the guest starring the group of veterans was discussing their individual talents, the female said she was a medic with the Marines. The Marines do not have medical personnel. Enlisted Navy personnel are assigned to Marine units and are called corpsmen. Only the Army and Air Force have medics.
After Steve shoots the last Santa on the roof, a close up of Steve's gun shows the hammer is down. Immediately after shooting it, the hammer would be back in the fully-cocked position. It is highly unlikely he would have de-cocked the gun while still aiming at the Santa.