This line revolves around a double entendre:
Slot machines, the staple of every casino, typically have an “arm” which you pull to start the machine after you’ve deposited your money (which you’ll probably never see again). If you’re lucky, you’ll make money!
Chop, however, pulls a different type of arm to get his money (he pulls out a gun and robs yo ass):
C-notes are $100 bills.