Ok, I'm not sure if this only work's on Xbox, or both ps3 and Xbox
But...
Step 1. Load up Bo1 and go on Multiplayer.
Step 2. Go onto theater mode.
Step 3. Once you're on theater mode go on community then scroll down three and it should say " real xp lobby " click on that and wait for it to download.
Step 4. Once it's downloaded play it and after a minute or so you will see blue writing at the bottom of you're screen.
Step 5. Once you got the blue writing go onto multiplayer and go into Team Tactical.
Step 6. Once you're in the lobby you'll see other people are level 1 aswell which means there doing the glitch aswell, once the game loads up in a match kill you're self and it should say something like 2-4cfduudef or something if it does kill you're self another 2 times... And you'll rank up to level 50
Step 7. Once it say's you're level 50 do NOT leave or the rank will not count. You need to wait until you're the host of the game to leave and you're rank will stay, most other people should be doing the glitch aswell so you should become the host fairly quick
Step 8. Once you're host leave! And wallaaa you're rank 50.
You'll know if you're host as when the previous host left after the host migration quickly look at the leaderboard and the person with the four bar will be host and should leave so he can get the level 50.
Also you do not get banned for this!