This glitch/cheat allows you to get unlimited ammo from the ammo dispensers found around in the operation:anchorage simulation and is very easy to do.
You can easily get as much ammo as you want. Simply get the ammo from the dispenser, drop it from your inventory and activate the dispenser again. You can do this as long as you want. This exploit, coupled with the ability to "glitch" items out of the simulator (through the gary 23 glitch (also explained) before the mission) allows you to carry inordinate amount of any available ammunition type out into the real world, so if you are using the glitch, stock up!
NOTES : Don't waste too much time during "guns of anchorage" doing this cheat since once that part of the sim is over and "paving the way" begins all your inventory will be cleared and you'll lose all the ammo you've accumulated thus far. From "paving the way" and on , go nuts since all the ammo you accumulate can be transfered to the "real-world" through the "gary 23" glitch.
The ammo dispensers only refill the following ammo types : .308 Caliber Round , 10mm Round , 5mm Round , 5.56mm Round , Flamer Fuel , Shotgun Shell.
The "gary 23" glitch in a nutshell is simple , find his body and place it inside the pod before going in the simulation (or kill all the outcasts and place their bodies in the pod) this is the only way to transfer the ammo you've accumulated in the sim to the "real-world". The "gary 23" glitch is further explained in detail , in the secret section of this website under the name "gary 23 glitch".