This tutorial is a very easy and fast way to get $99 mil and duplicate any weapon.
First you will need two controllers as this will be done in a split screen game, you will also need a USB or you can use the cloud to save your stuff.
Player one (controller 1) will be getting and providing the items. Player two (controller 2) will be sending the duplicated money or weapons. Now for the step by step tutorial on how to do it.
1. Drop any weapon you want to duplicate on the ground and have player 2 pick them up, trade all of you money to player two.
2. Now with controller 2 (player two) press start, then press "X" and change your storage device to either your USB or the cloud (if the second account is gold, this is the save that you will use to duplicate money or weapons). Now keep pressing "B" until you are given a choice to leave the game, save and quit.
3. Reload player two using the same save device that you just saved it on. Now send all guns and money to player one.
4. Now change your save device to your Xbox hard drive and then save and quit.
5. Reload player two again using your USB or cloud save device and drop all weapons and send all money to player one again.
Just do steps 4 and 5 over and over again until you get the desired amount of money. If you want to duplicate more money at a time just have player one send all of their money to player two and then follow step 2 again then steps 3-5 then repeat steps 4 and 5.
If you have any questions please feel free to ask. Also if this was already posted then I apologize. I didn't find any tutorial for split screen so I went into a game and eventually found a duplication glitch.