Before you max-out completely everything on the gun start with capasity! max that out and comtinue with the game. use up all the ammo in the gun so there is a red 0. do not reload your gun. then max out everything else then (firepower and reload speed and added stuff on depending on the gun. after beating the game and maxing out your gun go to Bonus Features! then scroll to the bottom of the list so you can see the name of the gun eg. H&K MP5 and the number 8 on its side. purchase the gun and wallah. a gun with infinate ammo that is not loaded.

i used H&K MP5 on purpose cuz this the gun i have with infinate ammo and not loaded