[mjk0011]

what you have to do is to join/host a game of attack and defend with friendly fire on or it wont work. make sure there are no restrictions so its 100% that u can get breach charge.
when you join/host a game invite a friend to play get them to change their equipment so they have breach charge and anything else.
(make sure there are no grenades, C4, or incendary available ie: restrict em)
make sure u and ur friend are on the defenders team.
spawn in the vault, go to the bottom door of the back stairs get ur friend to stand in front of it ready to plant a breach charge.
tell him/her to plant it but as they plant it u shoot em dead. to make sure u did it right go to the door and if it sez door busy its worked.
the assault team wont be able to plant breach charge to blow it open because the game thinks some1 else is doing it and with C4, grenades and incendary available they wont be able to blow it open. you dont have to do it right at the beginning of a game either. you could try and get the package carrier to die in the security room and "breach the doors there"
dont do it to wooden doors because you can just shoot the handles off or blow the door down anyway.

MJK1993

it also works 100% on the PS3 for any PS3 users