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Hi Ocskylla the way i found easiest to learn Quick shooting is to Make a save with the pistol and magnum in inventory load the save and input the infinite ammo cheat ( In the inventory press Up, Up, Down, Down, Left, Right, Left, Right, Aim.) for the magnum the way i did it was once the first shot goes off i started to spam the aim key as the weapon was reaching the original starting point this way you don't need to spam non stop, so when you are doing this with infinite ammo just keep trying over and over again. watch the Magnum when first shot goes off follow it down and spam when it gets close to original starting point... best i could do to help you, Hope this will help

All weapon upgrades collected