The reason as to why this glitch is so much better, is because you can get the same amount of kills in HALF the amount of time without destroying your KD.

Requirements
A friend
Both of you must have two controllers

BEFORE DOING ANY OF THIS, MAKE SURE BOTH OF YOUR SECOND CONTROLLERS ARE SIGNED INTO THE GUEST ACCOUNT, BUT WHEN IT SAYS "PRESS A TO PLAY", JUST LEAVE IT AT THAT

Step 1
Have your friend invite you to a player match, you accept his invite so you're both in the party.

Step 2
Have your friend quickly switch to Private Match, then to Combat Training. After he does this, he must back out.

Step 3
You will get an error, this is supposed to happen. Wait another second or two and it will switch the lobbies and show a different error/notice, hit "OK".

Step 4
Invite your friend back into the lobby. It will show both of you in a Player Match with your Combat Training ranks, this is normal.

Step 5
Switch the lobby to Wager Match, then quickly back to Player Match. After doing this back out by simply pressing B. Your friend will now be in a messed up Player Match lobby, this is also normal.

Step 6
Some of the steps in this part aren't necessary, but I like to do them just in case.

First, after you back out after the last step, select Xbox LIVE and go to Private Match. Change the map to Nuketown and the game mode to S&D. Go to Change Setting, General Options, Lives & Health Options and change the lives to unlimited. Back out of all the setting and press A on your second controller until it says your gamertag twice, one being yours and the other being the guest account. Go back onto the setting you were on and hover over Lives & Health Options.

Step 6
Have your friend invite you in whilst your hovering over that, accept his invite.

The next few steps must be done at a fast-enough speed

Step 7
Your friend must now back out of the messed up lobby you're both in, (you'll show as matched players to eachother). When he backs out he must "Press A to Play" on his second controller, and whilst he's doing that you need to invite him in before the game starts. Therefore on one team, it will be "Yourgamertag" and "Yourgamer(1)", on the other it will be "Hisgamertag" and "Hisgamer(1)".

Now the game will start, choose a class on your other controller and that way you can kill each other's second controller and still get XP