From WikiGTA - The Complete Grand Theft Auto Walkthrough
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GTA San Andreas
Liberty City Stories
The tec-9 is the weakest machine gun in GTA, but its low price makes it the weapon of choice of many gangs. The magazine of the tec-9 can hold 50 rounds. You can shoot while you're walking.
In GTA San Andreas, you can wield two weapons at once when you have reached the 'hitman level'. You reach the 'gangster level' at 10% weapon skill, and 'hitman level' at 100%.