Question about Surefire G2 Flashlight

I've got a Surefire G2 (see below) that I can't get to work. I pulled the batteries and they're putting out a total of 5.5 volts.

I have continuity on the blub from the outer spring to the inner spring. I even ordered a new bulb and it still won't light.

I haven't tried new batteries, but isn't 5.5v enough?

Any ideas?