DarthKermit:
I've used auger bits, spade bits and bi-metal hole saws.
Bi-metal hole saws are the only one of the above that will cut thru steel such as nails. They are rather short so you'll need extensions to get a reasonable distance down your walls, assuming you're doing so with the gib in place.
Ta. Do I want to know what the flail thing at the top of the picture is?



