Unverified, subject to be patched.

1) Empty your weapons inventory; guns only (not grenades), via the "throw down weapon" button, or by entering "gimmegun turret" in the text dialog for each weapon.

2) Once you are sure you don't have any available weapons, type "gimmegun turret_street" into the text dialog and hit enter.

3) You should then see a "Giving Weapon" confrimation, at which point you should hit the enter key twice in rapid succession, kind of like double clicking with a mouse.

4) The minigun should appear in your empty hands, with unlimited ammo.

*Also* If you attempt to pick up any other weapons you will lose the minigun, and will have to rid yourself of any weapons and reenter the code to get the minigun back.

Crawling through vents that have a grate blocking your exit cannot be broken while the minigun is equipped, and you cannont throw down the minigun, so you have to enter a cheat "gimmegun ----" for a gun to break the grate blocking your path.