The selection of weapons provided in Grand Theft Auto III consists of firearms and explosives, with the addition of two forms of mêlée attacks (hand-to-hand combat and baseball bat).
The weapons themselves are largely similar to the selection of weapons from Grand Theft Auto 1 and Grand Theft Auto 2, such as the pistol, the machine gun (which has been expanded to include a Micro Uzi submachine gun, an AK-47 assault rifle and an M-16 assault rifle in GTA III), the rocket launcher and the flamethrower from GTA1, and the shotgun and thrown weapons (Molotov cocktails and grenades) from GTA2. The weapons weren't categorized, so a player could have all weapons at the same time, meaning that the weapon selection system in GTA III, and in most other GTA games, involves hammerspace.
The porting of GTA III into a three dimensional environment also allowed for the inclusion of the sniper rifle and first-person aiming using the assault rifle and rocket launcher. In addition, it becomes possible in the game to perform drive-by shooting using the Uzi. The inclusion of magazine-based weapons also introduces the need to reload weapons after a magazine of ammunition is depleted. Additionally, wielding certain weapons would now restrict movement of the player. Weapons may be purchased from local firearms dealers and businesses, retrieved for free from certain dead gang members, mission-specific characters and law enforcers, or picked up in certain spots in the city.
The console versions of the game allowed the player to auto-aim with the push of a button, holding human targets at gun point using most firearms, with the exception of first person aiming for the sniper rifle, M-16 and rocket launcher, which are controlled by the analog stick as the player presses the same auto aim button. With the release of the PC version, a different control method was adopted; free aiming with the mouse. Because the PC version allows the player to aim targets with a mouse, the auto-aim system was removed. This control difference, named 'Standard' controls, is also seen in the console and PC ports of Vice City and San Andreas. The player can change to the control format of the PlayStation 2 in the control options by setting the option to Classic. This can be useful for experienced PS2 players who have a PS2 (or clone) controller hooked up, and also to exploit the fast shotgun bug in GTA III.
On both the PS2 and PC versions (and possibly the Xbox), a bug exists where the player can quickly fire slow weapons, such as the shotgun, without waiting to reload. On the PC, you must change the controls to Classic mode.
Target a person with the R1 or equivalent button, shoot and quickly release R1. Continue this and you can fire the powerful shotgun just as fast as the pistol. If any cars are in the way of your target they will blow up very quickly, so be careful. This is very useful for taking out gang members and law enforcement officers.