I have found out that the stated cheat codes can be written in any way one likes. For instance in the streets mission I wrote xxxx-xxxx-xxx and I had the M16 rifle. Or it could be anything starting with XXXX and the M16 is unlocked.
The border crossing mission does not carry over M16 and the mission is too long - one mistake and you are back to wear you started, there are no saves and resume the game from the checkpoint. [by: Jeddy]
To get the M16 A2 beat the game on blackops mode [by: jdog99]
2 GET BFG[249MACHINEGUN] FOR CITY STREET LEVEL.AT PROFILE!! DONT TYPE YOUR NAME.TYPE HQ6G-ZP3B-G5LE-WMXA OR FG65-WFZG-7MDP-PZGT THEN IT WLL LET YOU PUT IN YOUR NAME...PS DONT FOGET TO PUT THE ----IN THE CODE. [by: BOOGYMAN]
This is a INFINITE HEALTH CHEAT at the profile name maker put one of codes below.
760A-C290-0000-0000
2804-7FF6-0CA5-7A65
2804-7FOA-6416-8562
P.S. Don't know if this works. [by: Rc Dragon]