Mass Effect explains everything

Awkward Zombie

Pretty much true. For those who haven't partaken in the Mass Effect series (and boy, are you missing out!), all the tech does in one way or another rely on Element Zero and Mass Effect technology to function. Bit of a flaw, if you ask me. Anyone who could develop a weapon or device to neutralize Element Zero could potentially dominate the ME galaxy. Future plot device, anyone?

The guns don't really have infinite ammo, though. Instead of bullets, you stick a block of metal in the gun, which is equipped with a computer and microlasers. The computer cuts off small amounts of the metal, depending on the range of whatever you're trying to hit and other factors, and propels it using a Mass Effect field. In the first game, they tried to balance the lack of ammo consumption by having heat buildup if you fired a gun too much. Once the gun overheated, you had to wait for it to cool down sufficiently. In Mass Effect 2, they ditched that and replaced it with these clips that acted like disposable heatsinks, but unfortunately, and quite annoyingly, they became de facto ammunition, because guns wouldn't fire without them.