Richard Hammond's Crash Course programme, shown on BBC the other night, approx 45 minutes duration. He gets to drive an Abrams M1A2 tank, shoot the 50 cal and shoot the 120mm main gun. At approx 26 minutes there is an explanation of the rounds used with the 120mm main gun.
http://www.bbc.co.uk/iplayer/episode/b01mms3w/Richard_Hammonds_Crash_Course_Abrams_Tank/
http://www.bbc.co.uk/iplayer/episode/b01mms3w/Richard_Hammonds_Crash_Course_Abrams_Tank/