You are aware of the tactical cloak abuse where it comes to weight, right?
That is, if you break cloak as soon as you put it on, the cooldown will be about four seconds, no matter what weapons you're carrying. So yeah, infiltrator can carry Black Widow, Claymore and Typhoon, all at the same time and still don't suffer any from it.
No I was not aware of that bug, and I'm pretty sure it doesn't work that way in my game.
That is not a bug, it is an actual feature.
The Tactical Cloak cooldown shown in the GUI is the maximum cooldown of Cloak. The minimum cool down of cloak is always 3 seconds. So if you break Cloak early (after firing a weapon, for example), it will use a cooldown between the minimum cooldown and maximum cooldown, depending on how soon you break cloak after activating it.
Note that in cases where the maximum cooldown is greater than the minimum cooldown, the minimum cooldown (3 seconds) is used.
Note that cloak will remain active for 1 second before it breaks. So if you fire your gun when cloaked, cloak will break 1 second later. The damage bonus from cloak still applies for 1.5 seconds after breaking cloak.
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Oh, and why snipe with the Infiltrator? Shotguns are more fun.
CLAYMORE!