I got to play part in the Air Force OPFOR yesterday where we had to search out downed aircrew. They gave us all full auto M-4s and 13 magazines loaded with blanks and let us loose. We found about 9 aircrew members and went crazy with the full auto and simulated grenades. I also got to fire an M-60 on auto and an M-79 with sim grenades.
An interesting note is that the only magazines to cause a jam were the new restricted govt use only magazines.